How this calculator works
Concrete is estimated from length × width × thickness, with an optional waste allowance. The result is an estimate and may vary with the product, site conditions, measurement accuracy and installation method.
Before you use the estimate
- Measure the area carefully and keep units consistent.
- Review any waste allowance and material coverage assumptions.
- Check the product packaging or supplier specifications before purchasing.
Worked example
Frequently asked questions
How much concrete do I need for a 10×10 slab?
A 10×10 ft slab at 4 inches thick needs about 1.24 cubic yards before waste. Enter your own dimensions above — the calculator converts to cubic yards, bags and cost automatically.
How many 80-lb bags of concrete are in a cubic yard?
About 45 eighty-pound bags make one cubic yard, since each bag yields roughly 0.6 cubic feet. The calculator above converts your volume to bag counts for you.
Should I add extra concrete for waste?
Yes — 5–10% is standard for spillage and uneven subgrade. Use the waste field above and it is added to your total automatically. How to pick the right percentage →
How thick should a concrete slab be?
4 inches for patios and walkways, 4–6 inches for driveways that carry cars. Enter your thickness above in inches or feet — the calculator converts it automatically.
How do I order concrete from a supplier?
Order by cubic yards — that’s the “Your estimate” number above. Suppliers batch in quarter-yard increments, so round up and confirm the mix design with your plant.
How much does concrete cost per cubic yard?
Ready-mix concrete is usually priced per cubic yard and bagged concrete per bag — rates vary by location. Enter your local price in the price field above and the calculator applies it to your exact volume, including the waste allowance.
Should I buy concrete bags or order ready-mix?
For small jobs under about half a cubic yard, 80-lb bags from a home store make sense. For anything bigger, ready-mix ordered by the cubic yard is usually cheaper. The calculator shows both your yardage and bag count so you can compare.