Concrete calculator
Work out how much concrete to order — ready-mix by the yard or pre-mix bags — for a slab, patio, shed base or path.
Concrete Calculator
Cubic yards1.36
Cubic feet36.7
80 lb bags62
60 lb bags82
How we calculate
- Volume = length × width × (thickness in inches ÷ 12) gives cubic feet; divide by 27 for cubic yards.
- Add 5–10% for uneven ground and spillage.
- An 80 lb bag of pre-mix makes about 0.6 cu ft; a 60 lb bag about 0.45 cu ft.
Example: A 10 × 10 ft slab at 4 inches with 10% extra needs 1.36 cubic yards — about 62 bags of 80 lb.
Formulas and typical values last reviewed . Results are estimates — confirm quantities with your supplier.
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Frequently asked questions
How thick should a concrete slab be?
4 inches for patios, paths and shed bases; 5–6 inches for driveways or heavy loads.
Bags or ready-mix truck?
Under about 1 cubic yard, bags are practical. Above that, ready-mix delivery is usually cheaper and much less work.
How much does a yard of concrete weigh?
About 4,000 lb (2 US tons) per cubic yard.
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