Concrete Calculator
Quick answer: Concrete volume for a slab is length × width × thickness. A 5 m × 4 m slab that is 0.1 m thick needs 2 m³; add about 10% for wastage and order 2.2 m³.
Use the Concrete Calculator
Concrete formula and what each symbol means
Volume = length × width × thickness. Order quantity = volume × (1 + wastage). 1 yd³ = 27 ft³.
| Symbol | Meaning |
|---|---|
| length, width | Slab size |
| thickness | Slab depth |
| wastage | Spillage and uneven ground, often 5% to 10% |
Concrete examples
Metric
5 m × 4 m × 0.1 m = 2 m³. With 10% wastage: 2 × 1.10 = 2.2 m³.
Imperial
20 ft × 15 ft × 4 in (0.333 ft) = 100 ft³ = 3.70 yd³. With 10% wastage: about 4.07 yd³.
How to calculate Concrete step by step
- Measure length, width and thickness in the same unit.
- Multiply to get volume.
- Add 5% to 10% for wastage.
- Convert to the unit your supplier sells in.
How to read your Concrete result
Round up to the next supplier increment. Under-ordering mid-pour can cause weak cold joints.
Common mistakes when calculating Concrete
- Mixing inches with feet for thickness.
- Skipping wastage and uneven subgrade.
- Forgetting footings and edge thickening.
Concrete FAQ
How do I calculate concrete for a slab?
Multiply length by width by thickness in the same unit, then add 5% to 10% extra.
How many cubic feet are in a cubic yard?
27. Divide cubic feet by 27 to get cubic yards.
How thick should a concrete slab be?
Garden paths often use 75 to 100 mm (3 to 4 in). Driveways and garage floors usually need more. Check local code and ask an engineer.
How much extra concrete should I order?
Most people add 5% to 10% for spillage and uneven ground.
Method, review and disclaimer
Edited by: Hemant Kumar and Anjita Rai, founders of ToolsVault (SEO and content professional, not a licensed adviser). Method: this tool runs in your browser using the formula shown on this page; the numbers you enter are not sent to our servers.
Disclaimer: Estimate only. Structural work must follow local code and an engineer's design.