Concrete Calculator
Find the cubic yards to order, or how many bags to buy, for a slab, footing or post hole.
| Concrete needed | 1.36 cubic yards |
|---|---|
| Cubic feet | 36.67 |
| Cubic meters | 1.04 |
| 80 lb bags (0.60 cu ft each) | 62 |
| 60 lb bags (0.45 cu ft each) | 82 |
How to use it
- Choose a slab or a round column.
- Enter the size. Slab thickness is in inches (a typical patio is 4 inches).
- Keep some extra for uneven ground and spillage; 5% to 10% is a common allowance.
Formula
Slab volume (ft³) = length × width × thickness (in) ÷ 12Column volume (ft³) = π × (diameter (in) ÷ 24)² × heightCubic yards = cubic feet ÷ 27- Bags = cubic feet ÷ bag yield (0.60 ft³ per 80 lb bag, 0.45 ft³ per 60 lb bag), rounded up
Example
A 10 ft × 10 ft patio 4 inches thick is 10 × 10 × 4 ÷ 12 = 33.33 ft³, or 1.23 cubic yards: 56 bags of 80 lb mix. With 10% extra it is 36.67 ft³ (1.36 yd³), or 62 bags of 80 lb mix or 82 bags of 60 lb mix.
Questions
Bags or ready-mix truck?
Bags make sense for small jobs like post holes and small pads. For about a cubic yard or more, many people price ready-mix delivery; ask suppliers about minimum orders.
Where do the bag yields come from?
An 80 lb bag of standard concrete mix yields about 0.60 ft³ and a 60 lb bag about 0.45 ft³. Check the yield printed on the brand you buy.
How thick should a slab be?
4 inches is common for patios and walkways; driveways are often thicker. Follow local code and the project plans.
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Last reviewed 2026-10-11. Found a mistake? Tell us.