Concrete Planning Help

This article covers Concrete Planning Help, with practical UK guidance, examples and key points to consider before planning or ordering materials.

Which Guide Should I Use?

There are four guides available. Use the descriptions below to choose the right one for your project. If you are unsure which BS 8500 concrete mix your project needs, always start with the BS 8500 Mix Finder before using the Ready-Mix or Cement guides.

Cement Guide — Step-by-Step Guide

The Cement Guide is found on the Materials Cost Breakdown page under the first section. It determines exact material quantities and costs for site-mixed concrete and mortar using standard UK mix ratios.

Step-by-Step Instructions

• 1 Select Your Mix Type Tap or follow one of the six mix options at the top of the guide:

  General Concrete (1:2:4)General-purpose foundations, post holes, pads and bases. Approximately equivalent to GEN3/C20.
  Strong Concrete (1:1.5:3)Higher-strength applications, oversite, structural bases. Approximately C25/C30.
  Paving Mortar (1:5)Semi-dry bedding mortar for flag paving and slab laying. Uses building sand.
  Pointing Mortar (1:4)Jointing mortar for paved areas. Uses building sand.
  Render / Screed (1:3–1:4)External render scratch coat or floor screed. Uses sharp sand.
  Strip Foundation Lean Mix (1:3:6)Lowest-strength mass fill. Approximately GEN1. If you are unsure which mix to use, General Concrete (1:2:4) is correct for the majority of domestic site-mixed concrete applications.

• 2 Use your measured dimensions EnterLength (m)andWidth (m)the plan dimensions of the area you are concreting. EnterDepth (mm)the thickness of the concrete layer in millimetres. Most common depths: foundations 300–450mm, floor slabs 100–150mm, paving bed mortar 25–50mm, post holes 200–400mm below post base. Always measure in the same units. The guide expects length and width in metres and depth in millimetres — do not mix units.
• 3 Set the Waste Allowance The waste allowance choices adds a percentage to your net determined volume to account for spillage, uneven sub-base depth, mixing losses and material left in the mixer. Options:5%, 8%, 10% (default), 12%, 15%. Use10%for standard rectangular pours with a consistent depth. Increase to12–15%for irregular shapes, sloped ground or deep trench work where true depth is uncertain. Never use 0% or 5% for on-site work. Even precise measurements result in waste from mixing equipment, spillage and normal depth variation.
• 4 Select Your Region The region factor adjusts material costs for your UK location. Prices inLondon and the South Eastare typically 8–15% higher than the national average.Scotland and Northern Englandare typically at or slightly below average. Select the region nearest your project for the most accurate cost estimate.
• 5 Press Work out and Read Results Press the purpleWork out →options. The results panel shows: net and order volume, number of 25kg cement bags, tonnes and bulk bags of each aggregate, estimated water quantity, individual material costs and total material cost range. The cost range (±8%) reflects real-world price variation between suppliers. The result panel scrolls into view automatically on mobile. On desktop it appears immediately below the options.

Worked Example — Garden Wall Foundation

Results

Site-Mixed Concrete Is NOT Suitable for External Driveways or Patios

The Cement Guide is designed for foundations, mortar beds, post holes, render and internal slabs. External driveways and patios require BS 8500 PAV1 or PAV2 ready-mix concrete with mandatory air entrainment — a property that cannot be achieved by drum mixer or hand mixing. Use the Ready-Mix Concrete Guide instead for all external horizontal surfaces exposed to freeze-thaw conditions.

Ready-Mix Concrete Guide — Step-by-Step Guide

The Ready-Mix Guide is found on the Materials Cost Breakdown page under the second section. It is designed for ordering certified ready-mix concrete from a batch plant for any BS 8500 designated mix application.

Step-by-Step Instructions

• 1 Select Your BS 8500 Mix Choose from the eight available mix designations in the choices. If you are unsure which mix to select, use theBS 8500 Mix Finderfirst (separate resource on the BS 8500 Quick Reference page). Common choices:

  GEN1Strip foundations, trench fill, oversite
  GEN3Domestic garage floor (internal, not exposed to frost)
  RC28/35Reinforced ground floor slab, domestic extension
  PAV1Driveways, patios, paths — no regular de-icing salts
  PAV2Road-adjacent driveways, regularly salted areas
  FND3Sulfate-bearing ground (DC-3 soil classification)
  C40Heavy-duty industrial floors, severe structural exposure Always use the BS 8500 designation name when ordering — not old C-class names. Saying “PAV1 to BS 8500-1:2023” triggers the correct quality assurance and air entrainment system at the plant.

• 2 Enter Slab Dimensions EnterLength (m),Width (m)andDepth (mm). For irregular shapes, break the area into rectangles, work out each separately and add the volumes. Minimum practical ready-mix order is typically 1.0 m³ — orders below 3.0–4.0 m³ attract a short-load surcharge (the guide adds this automatically).
• 3 Set Waste Allowance The standard waste allowance for ready-mix concrete is8%(default). This accounts for formwork tolerances, slight under-pouring and residual concrete in the truck drum. For complex shapes with multiple pours, increase to 10%. For simple rectangular slabs with accurate formwork, 8% is appropriate. Ready-mix suppliers charge by the m³ batched — not the m³ you actually place. Always add waste. It is much harder and more expensive to order a second load than to slightly over-order.
• 4 Select Region Ready-mix concrete prices vary significantly by region —London and South Eastprices are typically 15–22% above the national average due to higher batch plant running costs, greater demand and higher delivery costs.Scotland and Northern Englandare typically at or slightly below average. Select your nearest region for the most accurate estimate.
• 5 Add Optional Pump & Fibre Costs If the pour location is inaccessible by a standard ready-mix truck (e.g. rear garden, basement), you will need aconcrete pump. Enter the pump hire cost (typically £350–£600/day for a boom pump, £250–£450 for a line pump). Thefibre admixturechoices adds cost for polypropylene fibres (£8–£12/m³) or steel fibres (£22–£35/m³) to reduce plastic shrinkage cracking or enhance toughness. Polypropylene fibres are a cheap addition (£8–£10/m³) that significantly reduces plastic shrinkage cracking in PAV1/PAV2 slabs during hot or windy conditions. Always worth specifying for any external slab.
• 6 Press Work out and Review figure The results show: net and order volume, number of truck loads (7 m³ per truck), BS 8500 full specification string, price per m³, concrete supply cost, short-load surcharge (if applicable), fibre and pump costs, total cost and cost per m². The specification string in the figure is formatted to use directly when phoning your ready-mix supplier.

Aggregate Guide — Step-by-Step Guide

The Aggregate Guide is the third section on the Materials Cost Breakdown page. It determines tonnes and bulk bag quantities for six loose aggregate types across three supply formats.

Step-by-Step Instructions

• 1 Select Your Material Choose from the six material options:

  MOT Type 1Crushed granite or limestone sub-base for patios, driveways and paths. Always compacted.
  Sharp SandAngular grit sand for concrete mixing, block paving bedding and drainage. BS EN 12620.
  Building SandSoft sand for bricklaying mortar, render and pointing. BS EN 13139.
  20mm GravelStandard coarse aggregate for drainage and concrete mixing.
  Pea Gravel (10mm)For paths, soakaways and French drains.
  BallastAll-in 0–20mm aggregate for mixing with cement for general concrete. Each material has a different bulk density — the guide uses the correct density for each material when converting volume to tonnes. Do not apply a single density factor across all aggregate types.

• 2 Enter Area and Depth EnterLength (m)andWidth (m)for the plan area. EnterDepth (mm)thefinished, compacteddepth you require. For MOT Type 1, the guide automatically adds a 20% compaction allowance (i.e. you need to order 120mm of loose material to achieve 100mm compacted). Standard depths:

  MOT Type 1 sub-base:100mm (patios on stable ground), 150mm (driveways), 200mm (heavy vehicles)
  Sharp sand paving bed:25–50mm
  Decorative gravel path:50–75mm
  Soakaway drainage blanket:300–600mm

• 3 Choose Supply Format Select how you want the aggregate supplied:

  Loose Tipper LoadCheapest per tonne for large quantities (4+ tonnes). Delivered by 6-wheel or 8-wheel tipper. Requires access for an HGV and an area to tip onto.
  Bulk Bags (850kg)Most convenient for medium quantities (1–6 bulk bags). Pallet-delivered, stackable, easier to manage on tight sites.
  Handy Bags (25kg)Most expensive per tonne but no minimum order. For very small repairs or top-ups only. For quantities above 4 tonnes, a loose tipper load is almost always 15–30% cheaper per tonne than bulk bags. The break-even point where bulk bags become more economical is typically at 3 tonnes or less.

• 4 Select Region and Work out Select your UK region for regional price adjustment, then pressWork out →. Results show: net and order volume (inc. 10% waste), bulk density, tonnes required, number of bulk bags, supply format, unit price, order quantity and total cost range per m².

Worked Example — Patio Sub-Base

Results

Loose Load Alternative — Saves ~£225

At 9.5 tonnes, ordering a loose tipper load at approximately £57/t (Yorkshire) would cost approximately £542 delivered — a saving of approximately £358 vs bulk bags. For quantities above 5 tonnes, always request a loose tipper load quote from a local aggregate supplier alongside the bulk bag price.

BS 8500 Mix Finder — Step-by-Step Guide

The BS 8500 Mix Finder is on the BS 8500 Quick Reference page. It is the fastest way to identify the correct designated mix for any UK concrete application — use it before placing any ready-mix order or before engaging a structural engineer to confirm specification.

• 1 Select Application Type Choose your application from the choices. Options are grouped into four categories: External Surfaces (driveways, patios, footways), Foundations (DC-1 to DC-4 ground), Floors & Slabs (unreinforced house floors, reinforced slabs, garage and industrial floors) and General & Masonry (blinding, oversite, post holes, drainage, paving mortar). Select the option that most closely describes your pour. If your ground has not been investigated for sulfate content, select “Strip/trench-fill foundation (DC-1 soil)” only if you are confident the ground is undisturbed natural soil with no history of industrial use. If in doubt, select DC-2 (FND2) — the cost difference is small and the protection is significantly better.
• 2 Select Reinforcement Type Select whether the concrete will beunreinforced, havenominal/light reinforcement(e.g. a single layer of A142 or A193 mesh for crack control only) or befully reinforced(structural rebar designed by an engineer). Reinforced concrete requires a higher specification than unreinforced concrete in the same exposure class.
• 3 Select Consistence Class Consistence (workability/slump) is a property of fresh concrete — it determines how easily the mix flows and is placed. The standard class isS3 (100–150mm slump)for most floor slabs, driveways and general work. UseS4 (160–210mm)for trench fill (self-flowing into narrow trenches) or congested reinforcement. UseS1 or S2for kerb haunching, dry lean mixes and drainage work. Do not add water on-site to increase workability — this severely weakens the concrete.
• 4 Press Find Mix and Read the figure PressFind Correct BS 8500 Mix →. The result panel shows: full designation name, strength class, exposure classes, air entrainment requirement, consistence class, ST equivalent (where applicable), minimum cement content, maximum w/c ratio, maximum aggregate size, minimum cover requirement, certification requirement, indicative price per m³ and a list of typical applications from BS 8500-1:2023 Annex A. Copy the designation shown in the result tag (e.g. “PAV1 — BS 8500:2023”) and use this exact wording when calling your ready-mix supplier. This ensures the plant produces the correct certified mix with the right air entrainment and durability provisions.

Guide Formulas Explained

All four guides use the same core volumetric approach. The formulas below show exactly how each key figure is derived — these can be used to verify guide results or to manually work out quantities for irregular shapes.

Field-by-Field Glossary

Definitions for every measurement field and figure value across all four guides.

Troubleshooting Common Issues

Answers to the most frequently reported issues with the guides.

The most common cause of unexpectedly high results is entering the depth in the wrong unit. Depth must be entered in millimetres (mm), not metres. For example, a 100mm slab should be entered as “100” — not “0.1”. Entering “0.1” in the depth field (i.e. 0.1mm) would give an almost-zero result, while entering “1000” (1000mm = 1 metre) would give a very large result. Always check your depth entry first.

• Standard patio/driveway slab: 100–150 mm → enter 100 or 150
• Strip foundation: 300–450 mm → enter 300–450
• Paving mortar bed: 25–50 mm → enter 25–50
• MOT Type 1 sub-base: 100–200 mm → enter 100–200

Ready-mix trucks carry a maximum of 7 m³. When your order volume (including the waste allowance) is below the supplier’s minimum economic load threshold — typically 3–4 m³ — a short-load surcharge is added to cover the fixed cost of sending a partially loaded truck. the working method adds £115 for orders below 3 m³ and £65 for orders between 3–4 m³. To eliminate or reduce the surcharge:

• Increase slab dimensions slightly to bring the order above the 4 m³ threshold
• Combine pours — if you have two small sections to pour, pour them in one delivery
• Ask your local supplier their specific threshold — some have a 3 m³ threshold, others 4 m³
• Consider a volumetric (on-site mixing) concrete truck for small pours — these mix to the exact quantity required with no short-load charge

The Aggregate Guide applies a 20% compaction factor to MOT Type 1 — meaning it determines enough material to compact down to your required depth. For example, if you need 150mm compacted sub-base, the working method orders for 180mm of loose material. Additionally, the 10% waste factor is applied on top of this. So for a 24 m² patio at 150mm compacted: Net loose volume = 24 × 0.18 = 4.32 m³, Order volume = 4.32 × 1.10 = 4.75 m³ = approximately 9.5 tonnes = 12 bulk bags. These numbers are correct and necessary — do not reduce them. Over 40% of driveway and patio sub-base failures in the UK are caused by insufficient depth or inadequate compaction.

Yes — for a 1:2:4 concrete mix, the coarse aggregate (gravel) is twice the volume of the fine aggregate (sand). The mix ratio is 1 part cement : 2 parts sand : 4 parts gravel , so you always need twice as much coarse aggregate as fine aggregate. This is correct and reflects the standard mix proportions. In tonne terms, because sharp sand (1.6 t/m³) and 20mm gravel (1.55 t/m³) have similar densities, the coarse aggregate tonnage will also be approximately twice the sand tonnage. When converted to bulk bags (both ~850kg), you will therefore need approximately twice as many bags of gravel as sand for a 1:2:4 mix.

No — PAV1 and “C30” are not the same. This is a very important distinction. PAV1 is a BS 8500 designated mix that specifies C30/37 strength plus mandatory XF3 air entrainment (3.5–6% entrained air). “C30” is an old BS 5328 C-class strength designation that carries no air entrainment requirement . A supplier who quotes “C30” for a driveway may be providing a higher-strength mix but without the freeze-thaw protective air void system. A non-air-entrained C30 concrete will scale and spall on a UK external driveway within a few winters — regardless of its compressive strength. Always insist on the full BS 8500 designation: “PAV1 to BS 8500-1:2023, 20mm aggregate, S3 consistence” . Ask your supplier to confirm the mix is certified and air-entrained before accepting delivery.

Guide prices are national average estimates based on published UK market data for February 2026 . Real quotes will vary for several reasons:

• Supplier-specific pricing:Individual ready-mix plants and aggregate suppliers set their own prices. Two plants 10 miles apart can differ by 10–20% per m³.
• Access and delivery conditions:Narrow roads, restricted access, waiting time, pump hire and weekend/bank holiday surcharges all add to the base price and are not included in the guide.
• Volume discounts:Large orders (10+ m³, pallet quantities of cement) attract trade discounts not reflected in single-unit prices.
• Fuel and energy surcharges:Some suppliers add a variable fuel surcharge on top of the listed price.
• Regional variation within a region:“South East” covers a huge area — central London prices differ significantly from rural Kent or Sussex.

the working method is designed to give you a realistic budgeting estimate within ±15% of actual cost. Always get at least two quotes from local suppliers before committing to a project budget.

All four guides work on a single rectangle. For irregular shapes, use one of these approaches:

• L-shape:Divide into two rectangles. Run the guide twice — once for each rectangle — and add the results (bags, tonnes, cost). Remember to add the waste allowance only once, or use a slightly lower waste % (5–8%) on the second rectangle to avoid double-counting.
• T-shape or complex polygon:Divide into the minimum number of non-overlapping rectangles. Work out each separately and sum all figures.
• Circle (e.g. circular patio):Work out area manually as π × r² (where r = radius in metres), then use the guide’s formula: Volume = Area × Depth/1000. Enter a fictitious “square” that gives the same area — e.g. for a 4m diameter circle (area = 12.57 m²), enter 3.55m × 3.55m.
• Curved driveway:Estimate the area by multiplying the average width by the total length. Add 10–15% to the waste allowance to compensate for the approximation.

Cement bags are rounded up to the nearest whole bag because cement is sold in discrete units — you cannot buy 13.4 bags. Rounding down would leave you short of cement, which is the most critical and irreplaceable ingredient in the mix. It is always better to have one spare bag of cement (it stores well in a sealed bag for 3–6 months) than to run short during a pour.

Aggregate quantities are shown to two decimal places in tonnes because aggregates are sold by weight to any quantity from a single delivery — your supplier will weigh out exactly 0.83 tonnes of sharp sand if needed. Bulk bags are then determined separately by rounding up to whole bags, because like cement, you cannot buy part of a bulk bag. If the aggregate tonnes figure gives a part-bag remainder, always round up and return or use the excess for another project.

Accuracy, Limitations & When to Get Professional Advice

Understanding what these guides can and cannot do will help you use them correctly and avoid costly mistakes on site.

What the Guides Are Accurate For

• volume working:The volumetric formula (Length × Width × Depth) is mathematically exact for rectangular sections with a uniform depth. Accuracy depends entirely on the quality of your measurements.
• Cement bag counts:Based on well-established UK industry bags-per-m³ constants. Accurate to ±1 bag for volumes above 0.5 m³. For very small volumes (<0.2 m³), the result may be slightly over-estimated due to mixer and mixing losses dominating.
• Aggregate tonnes:Based on standard bulk density values from UK supplier specifications. Real-world density varies ±5–10% depending on moisture content and aggregate source — buy to the determined quantity and check before reordering.
• Ready-mix volume and truck loads:Direct from the volumetric formula — accurate to the precision of your measurement measurements.
• Cost estimates:Within ±15% of real-world quotes for standard projects in typical UK locations. Useful for budgeting and sanity-checking supplier quotes.

Known Limitations

• Limitation: Assumes uniform depth; Impact: Real sub-bases and trenches have variable depth — actual material use will exceed the determined minimum; How to Address It: Always use 10–15% waste allowance; measure depth at multiple points before ordering
• Limitation: Rectangular areas only; Impact: L-shapes, curves and polygons require manual area working or splitting into rectangles; How to Address It: Split irregular shapes into rectangles; work out separately and sum
• Limitation: No labour cost; Impact: All costs are materials-only — no allowance for groundworks, formwork, reinforcement, finishing or labour; How to Address It: Use the driveway or patio cost guide for fully-installed cost estimates including labour
• Limitation: No structural design; Impact: The guides specify materials but do not design slab thickness, reinforcement layout or bearing capacity; How to Address It: Engage a structural engineer for reinforced slabs, large pours or any load-bearing application
• Limitation: Prices are national averages; Impact: Real supplier quotes may be 10–20% above or below the guide estimate; How to Address It: Always get 2–3 quotes; use guide as a budget benchmark only
• Limitation: No ground investigation; Impact: The Mix Finder assumes you know your DC class — it cannot determine soil sulfate content; How to Address It: If sulfate-bearing ground is suspected, commission a soil investigation; default to FND2 when in doubt
• Limitation: Single pour assumed; Impact: Multiple lifts (e.g. mass concrete in deep trenches poured in layers) may require different mix or timing; How to Address It: For pours exceeding 500mm depth or requiring retarder, consult your ready-mix supplier’s technical team

When You Must Get Professional Advice

Do NOT Rely on These Guides Alone For:

(1) Any structurally critical element — suspended slabs, beams, columns, retaining walls, any element supporting loads from above. Always engage a structural engineer. (2) Any pour on potentially contaminated ground — former industrial land, brownfield sites, sites near fuel storage, colliery spoil. A soil investigation is required before specifying FND class. (3) Any work subject to Building Regulations — extensions, new-build dwellings, garage conversions. Your Building Control officer will require specification evidence. (4) Any heritage or listed building setting — specialist mortar specifications apply. (5) Pours adjacent to or over existing services — always check for underground pipes, cables and drainage before any groundworks.

These Guides Are Reliable For:

Budget planning and cost checking · Ordering material quantities for permitted development work (patios, driveways, garden walls, sheds and outbuildings not requiring Building Regulations approval) · Checking supplier quotes for reasonableness · Generating the correct BS 8500 specification string for a ready-mix order · Learning and training purposes · Quick quantity cross-checks on-site during delivery.

Units & Conversions Quick Reference

A reference table for the unit conversions most frequently needed when using these guides or ordering materials.

• Convert From: Millimetres (mm); Convert To: Metres (m); Multiply By: ÷ 1,000; Example: 150mm ÷ 1000 = 0.15m
• Convert From: Metres (m); Convert To: Millimetres (mm); Multiply By: × 1,000; Example: 0.15m × 1000 = 150mm
• Convert From: m³ (cubic metres); Convert To: Litres; Multiply By: × 1,000; Example: 2.5 m³ × 1000 = 2,500 litres
• Convert From: Tonnes (t); Convert To: Kilograms (kg); Multiply By: × 1,000; Example: 1.75t × 1000 = 1,750 kg
• Convert From: Kilograms (kg); Convert To: 25kg cement bags; Multiply By: ÷ 25; Example: 325 kg ÷ 25 = 13 bags
• Convert From: Tonnes; Convert To: 850kg bulk bags; Multiply By: ÷ 0.85; Example: 3.4t ÷ 0.85 = 4 bags (round up)
• Convert From: Feet (ft); Convert To: Metres (m); Multiply By: × 0.3048; Example: 10ft × 0.3048 = 3.05m
• Convert From: Inches (in); Convert To: Millimetres (mm); Multiply By: × 25.4; Example: 4in × 25.4 = 101.6mm
• Convert From: Square feet (ft²); Convert To: Square metres (m²); Multiply By: × 0.0929; Example: 100 ft² × 0.0929 = 9.29 m²
• Convert From: Yards³; Convert To: Cubic metres (m³); Multiply By: × 0.7646; Example: 3 yd³ × 0.7646 = 2.29 m³
• Convert From: £/tonne; Convert To: £/bulk bag (850kg); Multiply By: × 0.85; Example: £70/t × 0.85 = £59.50/bag
• Convert From: £/m³ (concrete); Convert To: £/m² (at 100mm); Multiply By: ÷ 10; Example: £145/m³ ÷ 10 = £14.50/m²

All Guides Work on Mobile, Tablet and Desktop

Every guide is fully responsive and designed for use on site from a phone. No app download required — open theMaterials Cost BreakdownorBS 8500 Quick Referencepage in any browser. Results are optimised for small screens with tap-friendly measurements. For offline use, save the page to your home screen using your browser’s “Add to Home Screen” option.

Guide Help FAQ

Common questions about how the guides work, how to interpret results and how to use the figures when ordering materials.

The waste allowance is included in the working method result — the “Order Volume” figure already has the selected waste percentage applied. The “Net Volume” figure (shown separately) is the theoretical volume without waste. When ordering from your supplier, use the Order Volume figure — this is what you should actually order.

For example: a 5m × 4m × 100mm slab has a Net Volume of 2.000 m³. With 10% waste, the Order Volume is 2.200 m³ — order 2.200 m³ (or round up to 2.25 m³ if your supplier only quotes in 0.25 m³ increments). Do not add further waste on top of the Order Volume figure.

The cost range represents ±8% around the central estimate — reflecting normal price variation between UK suppliers for the same material. For budgeting purposes:

• Use the upper figurefor a conservative budget or when you have not yet received a supplier quote. This ensures you do not underestimate costs.
• Use the central figure(midpoint of the range) for project comparison purposes or when you already have a supplier quote and want to cross-check it.
• Use the lower figureonly if you have already received a competitive quote confirming a price at or near the lower bound.

Remember that the working method costs are materials only — they do not include delivery charges (other than the ready-mix short-load surcharge), labour, plant hire, formwork, reinforcement or any other project cost.

The guides are designed primarily for domestic and small commercial projects (residential extensions, driveways, patios, farm buildings, small commercial hardstandings). They use standard domestic-scale pricing and typical domestic mix specifications.

For large commercial or civil engineering projects, the guides can still provide useful volume and quantity cross-checks, but you should be aware of the following limitations at scale:

• Commercial ready-mix pricing is negotiated on a project basis and can be 10–20% below the guide’s retail estimates for large volumes
• Large structural pours require designed concrete (not just designated concrete) with full mix design documentation from the supplier
• Commercial projects require formal concrete specification in accordance with BS 8500-1:2023 as part of the contract documents — not just a guide printout
• Aggregate quantities for large earthworks and sub-base construction are typically determined using CAD survey data and cut-and-fill volumes, not simple L × W × D estimates

For sloped areas where the concrete depth varies from one end to the other (e.g. a sloped driveway where the concrete is 100mm at one end and 180mm at the other to maintain a level surface), use the average depth :

• Measure the depth at the shallowest and deepest points
• Work out the average: (shallowest + deepest) ÷ 2
• Enter this average depth in the guide
• Increase the waste allowance to 12–15% to account for the depth estimation error

Example: A 6m × 3m driveway where the fall means concrete depth ranges from 100mm to 200mm. Average depth = (100 + 200) ÷ 2 = 150mm. Enter 150mm in the working method with 12% waste allowance. This gives a reliable ordering quantity for this scenario.

For very complex ground profiles with multiple changes in level, split the area into sections where each section has a reasonably uniform average depth, work out each separately and sum the results.

Net Volume is the theoretical volume of concrete or aggregate that would exactly fill your specified area to the specified depth — determined as Length × Width × (Depth ÷ 1000). It assumes perfectly flat and level formwork with zero losses.

Order Volume is the net volume multiplied by the waste factor you selected. This is the quantity you should actually order from your supplier. It is always larger than the net volume.

When speaking to a ready-mix supplier, quote the Order Volume . When completing a Building Control application or structural engineer’s specification, quote the Net Volume (the actual structural element volume). The distinction matters because your BC application should describe the as-designed element (net volume), while your supplier order must include waste allowance.

• Print to PDF:Use your browser’s Print function (Ctrl+P on PC, Cmd+P on Mac) and select “Save as PDF” as the destination. The result panel will print clearly.
• Share the page URL:The page URL remains the same after working — bookmark it to return to the same article (you will need to re-enter your values, as the guide does not save measurements between sessions).
• Copy results manually:The result panel contains all key quantities in a clear format — copy the values into a spreadsheet or notes app.

A save-to-PDF and email-results feature is planned for a future update.

the working method uses a standard ready-mix truck capacity of 7 m³ to work out the number of loads. For pours up to 7 m³ it shows “1 load” — for 7.01 m³ and above it shows “2 loads”, and so on. In practice, most ready-mix suppliers can deliver any volume up to 7 m³ in a single truck, and will dispatch multiple trucks for larger pours.

Important notes for multi-load pours:

• For pours above 7 m³, ensure your site can accommodate a second truck arriving while the first is being discharged — trucks cannot wait indefinitely without the concrete beginning to set
• For large pours (10+ m³), discuss delivery sequencing with your supplier — they will typically schedule truck arrivals at 20–30 minute intervals
• For very large pours requiring continuous placement (e.g. a raft foundation or large driveway), a pump is usually required — factor this into your budget using the pump hire field
• Waiting time charges apply if a truck has to wait more than the agreed discharge time (typically 30–45 minutes) — ensure your team and any reinforcement or formwork is fully ready before the first truck arrives

Open the Guides

Jump directly to any of the four guides covered in this guide.

For additional concrete quantity and estimating resources, you can also visit ConcreteCalcs.com.