Live project tool
Concrete Calculator
Estimate concrete volume with a waste allowance. Results update instantly as you type.
Need a price estimate?Open the Concrete Cost Estimator→Building Material Calculatorbuildingmaterialcalculator.com
Building Material Calculator toolsProject estimates made clearer
Transparent by design
How this estimate works
We calculate from the measurements you enter, apply the selected coverage or waste factor, and round purchasable items up where partial packages are impractical.
Unusual layouts, product tolerances, local codes, and site conditions can change the final quantity. Use product instructions and approved plans for the final order.
Concrete slab planning guide
How much concrete do I need?
For a rectangular slab, multiply length by width by thickness. Convert thickness from inches to feet, divide cubic feet by 27 to obtain cubic yards, and then apply the waste allowance you choose.
Net cubic feet
length × width × (thickness ÷ 12)Order cubic yardsnet cubic feet × (1 + waste ÷ 100) ÷ 27Verified example
A 9 foot by 9 foot slab at 4 inches thick has a net volume of exactly 27 cubic feet, which equals 1 cubic yard. With 10 percent waste, the order estimate is 1.1 cubic yards.
Net volume1 cubic yard
With 10% waste1.1 cubic yards
40 pound bags99 bags
60 pound bags66 bags
80 pound bags50 bags
How far does one cubic yard go?
| Slab thickness | Approximate coverage |
|---|---|
| 3 inches | 108 square feet |
| 4 inches | 81 square feet |
| 5 inches | 64.8 square feet |
| 6 inches | 54 square feet |
Bag yield assumptions
The bag estimates use approximate mixed yields of 0.30 cubic feet for a 40 pound bag, 0.45 cubic feet for a 60 pound bag, and 0.60 cubic feet for an 80 pound bag. Product yield varies, so use the value printed on the exact bag when making a final purchase.
Primary sources
- NIST Special Publication 811 for unit conversion guidance.
- QUIKRETE Concrete Mix Data Sheet for approximate package yields.
- Sakrete High Strength Concrete Mix for published bag sizes and yields.
Reviewed September 9, 2026
Common questions
Concrete Calculator FAQ
How much concrete do I need for a slab?
Multiply slab length by width and thickness after converting every dimension to feet. Divide cubic feet by 27 for cubic yards, then add the selected waste allowance.
How many bags of concrete are in one cubic yard?
Using approximate packaged mix yields, one cubic yard equals about 90 bags at 40 pounds, 60 bags at 60 pounds, or 45 bags at 80 pounds before waste. Always check the yield printed on the exact product.
How many square feet does one yard of concrete cover?
One cubic yard covers about 81 square feet at 4 inches thick, 64.8 square feet at 5 inches thick, or 54 square feet at 6 inches thick.
Should I add extra concrete?
A planning allowance can help account for uneven subgrade, form variation, spillage, and ordering increments. The correct amount depends on the site and supplier, so keep the waste field adjustable.
How much does a yard of concrete cost?
Concrete prices and delivery charges vary by location, mix, quantity, and supplier. Use the linked Concrete Cost Estimator with a current local quote instead of relying on a national default.
Reviewed September 9, 2026
Keep planning
