How many m³ of concrete do I need for a shed base?

A typical 3m × 2.4m shed base at 100mm thick needs approximately 0.72 m³ of concrete. With 10% wastage, order 0.8 m³. For small jobs like this, bagged premix (around 89 × 20kg bags) is often more practical than ordering a ready-mix lorry.

How much does a load of ready-mix concrete cost in the UK?

A standard 6m³ ready-mix delivery typically costs between £65-£85 per m³ (so £390-£510 per load) depending on the mix specification and your location. Most suppliers charge a minimum delivery fee of around £150-£200, so it is only cost-effective for jobs needing 1m³ or more.

How many bags of postcrete or premix equal 1m³?

You need approximately 111 × 20kg bags of premix concrete to make 1m³. Each 20kg bag makes roughly 0.009 m³ of mixed concrete. For anything above 0.5 m³ it is usually cheaper and easier to order ready-mix.

Should I add extra concrete for wastage?

Yes, always add 10% wastage for concrete work. Concrete is lost through spillage, uneven ground, over-excavation, and settling. For trenches in rough ground you may need 15-20% extra. Running short on a pour is a serious problem, so it is always better to over-order slightly.

What depth should a concrete slab be?

For a standard domestic shed base or patio slab, 100mm (4 inches) is typical. A garage base needs 150mm minimum, ideally with mesh reinforcement. Foundations for walls must meet Building Regulations Approved Document A — typically 225mm minimum depth concrete in the trench.

Concrete Volume Calculator — How Much Concrete Do I Need in m³?

Concrete Volume Calculator — How Much Concrete Do I Need?

Calculate the volume of concrete required for slabs, foundations, and footings. Get ready-mix loads or bag quantities for any shape.

Shape

Select the shape of your concrete pour

Length

Length of the slab

Width

Width of the slab

Depth

Thickness of the concrete

Include wastage allowance

Adds 10% extra — recommended for all concrete pours

Wastage Percentage

10% standard; 15-20% for rough ground or trenches

Price Per m³ (optional)

Enter your supplier price per cubic metre for a cost estimate

How We Calculate This

This calculator computes the volume of concrete needed based on the shape and dimensions you enter. It supports rectangular slabs, circular slabs, and trench/strip foundations.

The formulas

Rectangular slab: Volume = Length × Width × Depth
Circular slab: Volume = π × (Diameter/2)² × Depth
Trench/strip: Volume = Length × Width × Depth (same as rectangular, entered as trench dimensions)

Conversion to delivery quantities

Ready-mix lorries in the UK typically carry 6m³ per load. For smaller jobs, 20kg premix bags each produce approximately 0.009 m³ of concrete.

The 10% wastage allowance accounts for spillage, uneven ground, and over-excavation. This is the standard recommendation from most UK concrete suppliers and aligns with NHBC guidance for domestic construction.

UK Building Regulations

For structural foundations, refer to Building Regulations Approved Document A (Structure) for minimum concrete depths and widths. Strip foundations for standard domestic walls typically require a minimum of 225mm concrete depth, with trench depths varying by soil type.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Concrete Volume Calculator — How Much Concrete Do I Need?

How We Calculate This

The formulas

Conversion to delivery quantities

UK Building Regulations

Frequently Asked Questions

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