How do I convert concrete measurements into cubic metres?

Make sure every measurement is converted to metres before multiplying. For example, 50mm equals 0.05m, 75mm equals 0.075m, 100mm equals 0.10m, 125mm equals 0.125m and 150mm equals 0.15m. An area measuring 6m by 4m at a depth of 100mm requires 6 × 4 × 0.10 = 2.40m³. Concrete in the UK is normally ordered in cubic metres rather than cubic yards.

How much concrete do I need for a shed base?

Multiply the length of the base by its width and concrete depth. A shed base measuring 3m by 2.4m at a depth of 100mm requires 3 × 2.4 × 0.10 = 0.72m³. With a 10% allowance, the result is 0.792m³, so you would plan for approximately 0.79m³, subject to the supplier's ordering increments. The appropriate slab depth, sub-base and reinforcement depend on the shed, ground conditions and manufacturer requirements.

How much concrete do I need for a patio or driveway?

Use the formula area × concrete depth = concrete volume. A driveway measuring 5m by 3m at a depth of 150mm requires 5 × 3 × 0.15 = 2.25m³. Adding a 10% allowance gives 2.475m³. The calculator estimates quantity only. The concrete specification, slab construction, sub-base, drainage and reinforcement should be selected according to the expected loads and site conditions.

How do I calculate concrete for post holes?

For a round post hole, use the formula volume = π × radius² × depth. The radius is half the diameter. Multiply the result by the number of holes. Ten holes measuring 300mm in diameter and 600mm deep require approximately 0.424m³. With a 10% allowance, the requirement becomes approximately 0.467m³. Measure the actual holes where possible because excavated holes are rarely perfectly uniform.

How much concrete can a concrete lorry carry?

Large UK mixer trucks commonly have capacities of approximately 6m³ or 8m³. Smaller mini-mix services may deliver loads of approximately 1m³ to 4m³. Capacity varies by supplier, and a vehicle may not always arrive fully loaded. Check the vehicle width, height and weight, road and driveway access, distance to the pour, chute reach and whether a concrete pump is required before ordering.

How much is a yard of concrete?

One cubic yard of concrete is approximately 0.765 cubic metres. Concrete in the UK is normally measured, priced and ordered by cubic metre rather than cubic yard. The final price depends on the concrete specification, order volume, supplier, delivery distance, minimum-load charges and whether a concrete pump is required. Use the calculator's cubic-metre result when requesting quotes from UK ready-mix suppliers.

How long does concrete take to cure?

Concrete starts to harden within a few hours, but it continues curing and gaining strength for several weeks. You can usually walk on it after approximately 24 hours, depending on the mix and conditions. Light use may be possible after about seven days, while concrete commonly reaches most of its specified strength after approximately 28 days.

How many 20kg or 25kg bags of concrete do I need?

Divide the required concrete volume by the mixed yield of one bag, then round the result up to the next whole bag. Using typical calculator yields of 0.010m³ per 20kg bag and 0.011m³ per 25kg bag, 0.10m³ requires approximately 10 bags of either size. A volume of 0.25m³ requires approximately 25 20kg bags or 23 25kg bags. A volume of 0.50m³ requires approximately 50 20kg bags or 46 25kg bags. One cubic metre requires approximately 100 20kg bags or 91 25kg bags. Bag yields vary by manufacturer and product, so check the yield printed on the packaging before purchasing.

Concrete Calculator

Q: How much extra concrete should I allow for wastage?

An allowance of approximately 5% to 10% is suitable for many projects. Use around 5% when the dimensions and formwork are accurate. Consider 10% where there is uneven excavation, variable depth, irregular formwork, spillage or difficult site access. For a calculated volume of 2.00m³, a 5% allowance gives 2.10m³ and a 10% allowance gives 2.20m³.

Calculate how much concrete you need in cubic metres for slabs, patios, driveways, shed bases, footings, walls, columns and post holes. Enter your measurements, select a waste allowance and get the required volume, estimated weight, bag quantity and ready-mix amount.

Measurement system:

Enter dimensions in metres, centimetres or millimetres

Waste allowance

Extra allowance for spillage and site variation

Concrete density

Typical normal-weight concrete is 2,300–2,400 kg/m³; use supplier data when available

Packaged concrete preset

Choose a typical UK bag or enter your product data

Bag weight

Dry product weight shown on the bag

Yield per bag

m³

Use the fresh-concrete yield stated by the manufacturer

Concrete required

Estimated concrete weight

0.0

tonnes

Density = 2400.0 kg/m³

Bag estimate

Selected product 20 kg ready-mix

Yield per bag 0.010 m³

Bags required 0

Total dry product 0 kg

Bags are rounded up. Verify the yield printed on your product before ordering.

How much concrete do I need?

Concrete volume is calculated by multiplying the length, width and depth in metres.
Concrete volume (m³) = length × width × depth
For example, a slab measuring 4 m long, 3 m wide and 100 mm deep requires 1.2 m³ of concrete. With a 10% allowance for spillage, uneven ground and formwork variation, the amount to order would be approximately 1.32 m³.

Introduction

Not sure how much concrete you need for your project? Our free UK concrete calculator provides a quick and reliable estimate for concrete slabs, walls, footings, strip foundations, stairs, kerbs, shed bases, and square or circular columns. Simply select the required shape, enter your measurements, and the concrete volume calculator will calculate the amount needed in cubic metres, cubic feet and cubic yards.
The tool also works as a concrete bag calculator, helping you estimate the number of common 20 kg and 25 kg ready-mixed concrete bags required for smaller jobs. For larger projects, you can use the cubic metre result when ordering ready-mix concrete from a UK supplier.

The built-in concrete weight calculator estimates the total weight in kilograms, tonnes, pounds and US tons. You can also add a wastage allowance to account for spillage, uneven ground and variations in site measurements, reducing the risk of ordering too little.
Whether you are laying a garden path, pouring a patio, building a shed base or planning a larger construction project, this concrete estimator gives you a clear answer to the question: “How much concrete do I need?”

How to use this concrete calculator?

Steps	What to do
Step 1: Choose your shape	Select the shape that best matches your project. Use square or rectangular for concrete slabs, patios and shed bases; circular for post holes and round columns; or choose walls, strip foundations, footings, stairs, kerbs and other available shapes. For foundation work, the tool can also be used as a practical concrete footing calculator.
Step 2: Choose your unit system	Select either metric or imperial measurements. Metric units are commonly used on UK building projects, but you can choose whichever system matches your plans, drawings or site measurements.
Step 3: Input dimensions	Enter the required length, width, depth, height or diameter for your selected shape. You can use millimetres, centimetres or metres, depending on the measurements shown on your drawings or tape measure. Measure each dimension as accurately as possible to obtain a reliable concrete estimate.
Step 4: Add wastage allowance	Use the Wastage dropdown to include a small amount of additional concrete. This helps account for spillage, uneven ground, excavation variations, irregular formwork and concrete left in the mixer, chute or wheelbarrow. Adding a sensible allowance reduces the risk of running short during the pour.
Step 5: Select density	Choose the density that best matches your concrete mix. The default density of 2,130 kg/m³ is suitable for general estimating, so you can leave it unchanged unless your supplier or project specification gives a different value. Lightweight, reinforced or specialist concrete mixes may have different densities.
Step 6: Get results	Select Calculate to view the required concrete volume in cubic metres, cubic feet and cubic yards, together with the estimated weight in metric and imperial units. The concrete bag calculator also shows the approximate number of common 20 kg and 25 kg ready-mixed concrete bags required, helping you plan your order from a UK builders’ merchant without unnecessary guesswork or overbuying.

How to calculate concrete in cubic metres?

To calculate concrete volume, convert every measurement to metres and multiply the dimensions together.
For a rectangular slab:
Length × Width × Depth = Volume in cubic metres
A depth of 100 mm equals 0.1 m. Therefore, a slab measuring 4 m × 3 m × 100 mm requires:
4 × 3 × 0.1 = 1.2 m³
Adding a 10% allowance gives:
1.2 × 1.10 = 1.32 m³
Always round an order upward rather than downward and confirm the final quantity with your concrete supplier.

Worked concrete examples

Project	Measurements	Base Volume	With 10% allowance
Patio slab	4 m × 3 m × 100 mm	1.20 m³	1.32 m³
Shed base	3 m × 2.4 m × 100 mm	0.72 m³	0.79 m³
Driveway section	5 m × 3 m × 150 mm	2.25 m³	2.48 m³
Strip footing	10 m × 600 mm × 250 mm	1.50 m³	1.65 m³

Note: These dimensions are calculation examples, not structural design recommendations. The required depth, reinforcement and concrete specification depend on the project, ground conditions and approved design.

Calculation methodology

Volume is calculated using the geometric formula for the selected shape. Measurements are converted to metres before volume is calculated in cubic metres. The chosen waste allowance is added separately. Estimated weight uses a default normal-weight concrete density of 2,400 kg/m³. Bag calculations use the product yield entered by the user and are rounded up to whole bags.

Important
This calculator estimates material quantity only. It does not design structural elements, specify concrete strength, determine reinforcement or replace approved drawings, supplier advice or professional engineering calculations.

What is concrete?

Concrete is one of the most widely used building materials in the UK. It is made by mixing cement, sand, aggregate such as gravel or crushed stone, and water. When freshly mixed, it is workable enough to pour into formwork and shape to suit the job.
Once poured, the concrete starts to set and gradually becomes harder and stronger over the following days and weeks. It is commonly used for foundations, footings, driveways, patios, garden paths, floors, walls and columns.
A concrete calculator simply helps you work out how much concrete is needed to fill a particular area or shape. This makes it easier to order the right amount and reduces the chance of running short or paying for more than you need.

Concrete Mix Grades and Typical Uses in the UK

UK concrete grade	Approximate strength	What it means	Typical UK uses
GEN0 / ST1	Around 8-10 MPa	Low-strength, non-structural concrete	Kerb bedding and backing, drainage works, blinding layers and general non-structural fill
GEN1 / ST2	Around 10-15 MPa	General-purpose, unreinforced concrete	Strip footings, trench-fill foundations, oversite concrete, drainage works and concrete blinding
GEN2 / ST3	Around 15-20 MPa	Medium-strength concrete for general building work	Domestic floor slabs, shed bases, conservatory bases and other unreinforced internal floors
GEN3 / ST4	Around 20-25 MPa	Higher-strength general-purpose concrete	Garage floors, workshop floors and heavier-duty unreinforced slabs
C20/25	20 MPa cylinder / 25 MPa cube	Common structural-strength concrete	Reinforced foundations, floor slabs, beams and general
C25/30	25 MPa cylinder / 30 MPa cube	Stronger structural concrete	Reinforced slabs, columns, beams, retaining walls and light industrial floors

Comparison of different Concrete Types and Strengths

Lightweight Concrete

Lightweight concrete uses low-density aggregates to reduce the overall weight of the finished structure. It typically has a density of around 1,400–2,000 kg/m³, compared with approximately 2,300–2,400 kg/m³ for standard concrete.
Depending on the mix design, structural lightweight concrete commonly achieves strengths of around 20–40 MPa. It may be used for roof slabs, upper floors, precast panels and other projects where reducing the load on the structure is important.
Choose a lower concrete density in the calculator when the project specification specifically calls for lightweight concrete.

Standard / Everyday Concrete

Normal-weight concrete is the most commonly used type for domestic and general construction work in the UK. Its density is usually around 2,200–2,400 kg/m³, with 2,400 kg/m³ often used as a practical estimating figure.
Common strength classes include C16/20, C20/25 and C25/30, depending on the application. Normal-weight concrete is widely used for floor slabs, paths, patios, foundations, footings and general reinforced concrete work.
For most standard concrete calculations, this is the appropriate default density unless your supplier or project specification states otherwise.

High-Strength / Heavy Concrete

High-strength concrete is designed to carry greater loads than standard concrete. In UK and European classifications, it generally begins at around C55/67, although lower strength classes such as C30/37 or C40/50 may still be considered heavy-duty for many domestic or commercial projects.
It is commonly used for heavily loaded columns, structural beams, industrial floors, bridges and specialist engineering work. Its density may remain close to that of normal concrete, because higher strength does not necessarily mean higher weight.
Use the density and strength stated in the structural design or concrete supplier’s specification rather than assuming that stronger concrete is always heavier.

Concrete weight and density

Concrete weight is estimated by multiplying its volume by its density:
Weight = concrete volume × density
For general estimating, normal-weight concrete can be calculated using approximately 2,400 kg/m³.

For example: 1.5 m³ × 2,400 kg/m³ = 3,600 kg
This is approximately 3.6 tonnes.
Lightweight, heavyweight and specialist concrete can have different densities. Use the value supplied by the manufacturer or ready-mix supplier when it is available.

UK concrete specifications

Concrete in the United Kingdom is commonly specified in accordance with BS EN 206 and BS 8500. Depending on the project, the concrete may be described using designated, designed, standardised prescribed or proprietary specifications.

This calculator estimates the quantity of concrete required. It does not select the correct strength class, exposure class, consistence, cement content, reinforcement or structural dimensions.

For structural slabs, foundations, retaining elements or other safety-critical work, use the approved drawings and confirm the concrete specification with the designer, engineer, building control body or concrete supplier.

Bagged or Ready-Mix Concrete? What to order?

Bagged concrete can be convenient for small repairs, individual post holes and jobs with restricted access. Ready-mixed concrete is usually more practical for larger slabs, driveways and continuous pours where consistent supply is important.
When comparing the two options, consider:

The total volume required
Product yield per bag
Mixing time and labour
Supplier minimum order quantities
Delivery access
Concrete pump or barrow requirements
The time available to complete the pour

A common 20 kg ready-to-use concrete product may produce around 0.01 m³, which would mean approximately 100 bags for 1 m³ before wastage. Actual yields vary, so use the figure printed on the chosen product.

The “wastage allowance”

The wastage allowance is simply there to cover the small differences that happen on a real job. Ground is not always perfectly level, formwork can vary slightly, and some concrete will usually be left behind in the mixer, chute or wheelbarrow. Even with careful handling, a little spillage is normal.
For most projects, adding around 5% to 10% is a sensible starting point. The calculator applies your chosen allowance to the volume and then updates the weight and bag estimates automatically.
It is usually better to have a small amount left over than to run short halfway through the pour, especially when another delivery could mean extra cost and delays. Our concrete mix calculator does the same.

Frequently Ask Questions about Concrete Calculations

Make sure every measurement is converted to metres before multiplying:

50mm = 0.05m
75mm = 0.075m
100mm = 0.10m
125mm = 0.125m
150mm = 0.15m

For example, an area measuring 6m × 4m at a depth of 100mm requires:
6 × 4 × 0.10 = 2.40m³
Concrete in the UK is normally ordered in cubic metres rather than cubic yards.

One cubic metre of normal-weight concrete typically weighs approximately 2,300 to 2,400kg, or around 2.3 to 2.4 tonnes.
The calculator uses 2,400kg/m³ as its standard estimate. Lightweight, heavyweight and specialist concrete mixes can have significantly different densities, so supplier information should be used when available.

An allowance of approximately 5% to 10% is suitable for many projects.
Use around 5% when the dimensions and formwork are accurate. Consider 10% where there is uneven excavation, variable depth, irregular formwork, spillage or difficult site access.
For example:

Calculated volume: 2.00m³
5% allowance: 2.10m³
10% allowance: 2.20m³

The appropriate contingency depends on the shape, project size and actual site conditions. Major UK suppliers similarly advise allowing for imperfections in the pour rather than ordering only the exact theoretical volume.

Multiply the length of the base by its width and concrete depth.
For a shed base measuring 3m × 2.4m at 100mm deep:

3 × 2.4 × 0.10 = 0.72m³

With a 10% allowance:

0.72 × 1.10 = 0.792m³

You would therefore plan for approximately 0.79m³, subject to the supplier’s ordering increments. The appropriate slab depth, sub-base and reinforcement depend on the shed, ground conditions and manufacturer’s requirements.

se the same volume formula:
Area × concrete depth = concrete volume
For example, a driveway measuring 5m × 3m at 150mm deep requires:

5 × 3 × 0.15 = 2.25m³

Adding 10% gives:

2.25 × 1.10 = 2.475m³

The calculator estimates the quantity only. A suitable concrete specification, slab construction, sub-base, drainage and reinforcement should be selected according to the expected loads and site conditions. External paving may also require a mix designed for freeze–thaw exposure.

For a round post hole, use:

Volume = π × radius² × depth

The radius is half the diameter. Multiply the result by the number of holes.
For ten holes measuring 300mm in diameter and 600mm deep:

π × 0.15² × 0.60 × 10 = approximately 0.424m³

With a 10% allowance, the requirement becomes approximately 0.467m³.
Measure the actual holes wherever possible because excavated holes are rarely perfectly uniform.

Large UK mixer trucks commonly have capacities of approximately 6m³ or 8m³. Smaller mini-mix services may deliver loads between approximately 1m³ and 4m³.
Truck capacity varies by supplier, and the vehicle may not always arrive fully loaded. Before ordering, check:

Vehicle width, height and weight
Road and driveway access
Distance from the truck to the pour
Chute reach
Whether a concrete pump is required

A fully loaded mixer is a heavy vehicle, so access should be agreed with the supplier before delivery.

The price depends on your area, order size, and mix, but as a rough guide:

About $130–$200 USD per cubic yard for regular ready-mix (before delivery fees and taxes).

Concrete starts to harden in a few hours, but it doesn’t fully “cure” that fast.
You can usually walk on it after 24 hours. Light use after about 7 days and It reaches most of its full strength in about 28 days. So, it hardens quickly, but it keeps curing and getting stronger for weeks.

Divide the required concrete volume by the mixed yield of one bag, then round up to the next whole bag.
Using the calculator’s standard yields, with no additional wastage:

0.10m³: 10 × 20kg bags or 10 × 25kg bags
0.25m³: 25 × 20kg bags or 23 × 25kg bags
0.50m³: 50 × 20kg bags or 46 × 25kg bags
1.00m³: 100 × 20kg bags or 91 × 25kg bags

These estimates use a yield of 0.010m³ per 20kg bag and 0.011m³ per 25kg bag. If you select a waste allowance, the calculator adds it before calculating the bag quantity.
Actual yields vary by manufacturer and product, so check the yield shown on the packaging or enter a custom yield in the calculator.