Concrete Volume Calculator
Compute the concrete volume needed for a rectangular slab or footing.
Formula
Volume = length × width × thickness
Inputs
- Length (m)
- Width (m)
- Thickness (mm)
Notes and assumptions
- Calculates concrete volume only. Cement/sand/aggregate quantities depend on the specific mix design (e.g. M20, M25) and should be sized to your local concrete mix standard — this calculator does not estimate materials or replace a structural design review.
What it does
Concrete needed for a rectangular slab or footing: length × width × thickness.
Where it's used
Ordering ready-mix concrete for slabs, driveways and footings.
How to use it
- Enter length and width in metres.
- Enter the thickness in millimetres.
- Read the volume in m³ and add a margin for waste.
The formula explained
- V
- L × W × t (with t converted to metres)
Worked example
A 6 × 3.5 m slab, 125 mm thick.
Inputs:
- Length: 6 m
- Width: 3.5 m
- Thickness: 125 mm
The calculator gives:
- Result: 2.625 m³
- Liters: 2625
Tips and common mistakes
- Order about 5–10 % extra for uneven ground and spillage.
- Cement, sand and aggregate quantities depend on the mix design (e.g. M20).
- This is a quantity estimate, not a structural design.
Questions people ask
How many bags of cement do I need?
For a nominal M20 mix (1 : 1.5 : 3) a common rule is about 8 bags of 50 kg per cubic metre, allowing for the dry volume being about 54 % more than the wet. The 2.625 m³ slab needs about 21 bags — confirm with your supplier or engineer.
How much does the concrete weigh?
Normal concrete is about 2 400 kg per cubic metre, so the example slab weighs around 6.3 tonnes — worth knowing for delivery and formwork.
How thick should a slab be?
Ground-floor slabs and driveways are commonly 100–150 mm, but the right thickness depends on loads, soil and reinforcement. Use the thickness from your drawings or engineer.
Related Civil & Construction calculators
Enter your values to get the result with the formula, substituted values and an explanation of each step.