Last updated: October 2026
How much concrete do I need?
Short answer: multiply length × width × thickness (all in feet) for cubic feet, then divide by 27 for cubic yards. Add 10% waste and divide by 0.6 ft³ per 80-lb bag to get your bag count. The calculator above does all of it for slabs, walls and round columns.
How to measure for concrete
Slab: measure the length × width in feet and the thickness in inches — 4 inches is standard for patios, sidewalks and shed floors, 6 inches for driveways. Wall: measure the length × height in feet and the wall thickness in inches (usually 8). Round column: measure the diameter in inches and the height in feet. Enter any shape and the calculator returns the volume in cubic feet and cubic yards, plus the exact bag count for 80, 60 and 40-lb bags.
Bag yields and slab thickness
| Bag size | Concrete yield | Bags per cubic yard |
|---|---|---|
| 80 lb | 0.6 ft³ | 45 |
| 60 lb | 0.45 ft³ | 60 |
| 40 lb | 0.3 ft³ | 90 |
| Slab use | Recommended thickness |
|---|---|
| Sidewalk, patio, shed floor | 4 in |
| Driveway, garage floor | 5–6 in |
| RV pad, heavy equipment | 6+ in |
Bag yields vary slightly by manufacturer and mix. Round up and keep one extra bag on hand for touch-ups — concrete suppliers charge for part-loads on ready-mix, so accurate bag counts save real money.
Frequently asked questions
How much concrete do I need for a 10×10 slab?
About 1.23 cubic yards — that is 62 bags of 80-lb mix with a 10% waste allowance. Pour the same area 6 inches thick and it takes about 1.85 cubic yards (92 bags).
How much concrete does an 80-lb bag make?
One 80-lb bag of concrete mix yields about 0.6 cubic feet of hardened concrete. A 60-lb bag yields 0.45 ft³ and a 40-lb bag yields 0.3 ft³. The American Concrete Institute publishes the industry standards behind concrete mix design and testing.
How thick should a concrete slab be?
4 inches is standard for sidewalks, patios and shed floors. Use 5–6 inches for driveways and garage floors, and 6 inches or more for RV pads and heavy equipment.
How many bags of concrete are in a cubic yard?
About 45 bags of 80-lb mix per cubic yard (27 ft³ ÷ 0.6 ft³ per bag). With a 10% waste allowance, plan on 50 bags per yard.
Is my project data private?
Completely. Every calculation runs locally in your browser with JavaScript — your measurements are never sent to a server, stored, or tracked.