Concrete Calculator
Work out how much concrete you need for a slab, patio, footing, post hole, column or steps — in cubic yards and bags — before you order ready-mix or head to the store.
Free · No sign-upHow to use Concrete Calculator
- 1. Choose what you’re pouring: slab, footing, post hole or column, circular slab, tube or stairs.
- 2. Enter the dimensions — each has its own unit, so you can mix feet and inches.
- 3. Set how many identical pours and the extra for spillage (10% is common).
- 4. Read the cubic yards to order and the number of 40, 60 or 80 lb bags, plus weight and cost.
Frequently asked questions
How much concrete do I need for a 10 × 10 slab?
At 4 inches thick: 10 × 10 × (4 ÷ 12) = 33.33 cubic feet ÷ 27 = 1.23 cubic yards. With 10% extra that’s about 1.36 cubic yards, or 62 bags of 80 lb.
How many bags of concrete make a yard?
About 45 bags of 80 lb (0.60 cu ft each), 60 bags of 60 lb (0.45 cu ft) or 90 bags of 40 lb (0.30 cu ft) make one cubic yard. Check the yield printed on your bag.
How do I calculate concrete for a post hole?
Choose round column or post hole and enter the hole’s diameter and depth. Volume = π × (diameter ÷ 2)² × depth. Set How many to the number of holes; subtract the post’s volume if you want to be exact.
How thick should a concrete slab be?
4 inches is standard for patios, walkways and shed floors; 5–6 inches for driveways and garage floors that carry vehicles. Check local building codes for footings and structural work.
How much extra concrete should I order?
Add 5–10% for spillage, uneven ground and forms that bow. Ready-mix is usually sold in quarter-yard steps, and running short mid-pour is far worse than having a little left over.
How much does a cubic yard of concrete weigh?
About 4,000 pounds (roughly 150 lb per cubic foot). A 1.23 cubic yard slab weighs close to 5,000 lb, which is why bags make sense only for small jobs.