Concrete Calculator
Work out how much concrete you need for a slab, base or path, with extra for waste and an approximate weight.
New: please check your results.
- Concrete to order
- 1.32 m³
- Approximate weight
- 3,168 kg
What it does
Find the volume of concrete for a rectangular slab, base or path from its length, width and depth. It adds extra for waste and gives a rough weight, which helps when planning deliveries or mixing by hand.
How to use it
- Length
The length of the area to fill.
- Width
The width of the area to fill.
- Depth
How thick the concrete will be. Paths and patios are often around 75 to 100 mm; bases for heavier loads are thicker.
- Extra for waste
Extra to cover spills, uneven ground and slightly deeper spots. 5 to 10% is common. Set it to 0 for the exact volume.
Common uses
- Ordering ready-mixed concrete for a patio, base or driveway.
- Working out how much to mix by hand for a shed or garden base.
- Working out gravel or sub-base underneath.
- Working out other volumes.
The formula
Volume = length × width × depthTo order = volume × (1 + waste ÷ 100)Weight ≈ volume to order × 2,400 kg/m³Where:
- 2,400 kg/m³
- a typical density for normal concrete
Measure depth in the same units as length and width, or let the calculator convert it: depth in mm is converted to metres automatically.
Worked example
A slab 4 m long, 3 m wide and 100 mm deep:
- Volume: 4 m × 3 m × 0.1 m = 1.2 m³
- With 10% extra: 1.2 m³ × 1.1 = 1.32 m³
- Approximate weight: 1.32 m³ × 2,400 kg/m³ = 3,168 kg
Questions people ask
How much extra concrete should I order?
Most people add 5 to 10% for spills, uneven ground and slightly deeper areas. Running short partway through a pour is far worse than having a little left over.
What's the difference between cubic metres and cubic yards?
One cubic yard is about 0.76 cubic metres. Ready-mixed concrete is usually sold by the cubic metre in the UK and Europe and by the cubic yard in the US. Use the Convert box under the results to switch.
Is the weight exact?
No. It uses a typical density of 2,400 kg per cubic metre. The real weight depends on the mix, so treat it as a guide for planning.
Last checked 24 October 2026