Concrete calculator (m³ and cubic yards)
Enter length, width, thickness and how many identical pours you have to see how much concrete to order.
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How to use it
- Enter length, width, thickness, number of identical pours and waste allowance.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Volume = length × width × (thickness ÷ 100) × count, then × (1 + waste ÷ 100). 1 cubic yard = 0.764554857984 m³ exactly.
Example
Inputs: Length = 5 m, Width = 4 m, Thickness = 15 cm, Number of identical pours = 1, Waste allowance = 5 %. Result: Volume to order (with waste): 3.15 m³; Net volume: 3 m³; In cubic yards: 4.12 yd³.
Limits and caveats
- Assumes a rectangle of even thickness; split odd shapes into rectangles.
- The waste allowance is an estimate, usually 5% to 10% depending on the site and formwork.
Questions about this tool
How much concrete for a 100 m² slab 15 cm thick?
Multiply area by thickness in metres: 100 × 0.15 = 15 m³. With 5% waste that becomes 15.75 m³.
Why add a waste allowance?
Formwork bows, the ground is uneven and some mix stays in the pump, so ordering the net volume alone tends to fall short.
How many cubic metres are in a cubic yard?
One cubic yard is exactly 0.764554857984 m³, because the yard is defined as 0.9144 m.