How to use this calculator
- Enter or choose shape.
- Enter or choose units.
- Enter or choose how many.
- Enter or choose waste allowance.
- The cubic metres updates as you type. Use Copy result or Share to keep it.
Formula
Slab volume = L × W × T; column volume = π × (D ÷ 2)² × H; total = volume × quantity × (1 + waste %)
- L, W, H
- length, width, height
- T
- thickness
- D
- diameter
Worked example
- Thickness 10 cm = 0.10 m.
- Volume = 4 × 3 × 0.10 = 1.2 m³.
- In cubic yards: 1.2 × 1.30795 = 1.57 yd³.
A 4 m × 3 m slab, 10 cm thick, needs 1.2 m³ of concrete before any waste allowance.
What the result means
Order a little more than the net volume: ready-mix suppliers usually deliver in fixed increments, and running short mid-pour causes cold joints.
Assumptions and limits
- Metric inputs: length, width and height in metres; thickness and diameter in centimetres. Imperial: feet and inches.
- Does not account for reinforcement volume, sloped ground or formwork deflection.
- Bag counts depend on the product’s stated yield; check the packaging.
Questions
How much extra concrete should I order?
A 5–10% allowance is typical for slabs on prepared ground; more for uneven excavations.
Please note: Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials.