Concrete Calculator
Enter your slab or footing size to see cubic yards and the number of concrete bags to buy.
| Thickness | Cubic yards | 60 lb bags |
|---|---|---|
| 2 in | 0.62 | 38 |
| 3 in | 0.93 | 56 |
| 4 in | 1.23 | 75 |
| 5 in | 1.54 | 93 |
| 6 in | 1.85 | 112 |
How to figure concrete volume
Measure length and width in feet and thickness in inches. Multiply length by width, multiply by thickness divided by 12, and you have cubic feet. Divide by 27 for cubic yards, which is how ready-mix is sold.
Bags versus ready-mix
Bags make sense up to about a cubic yard, which is roughly 60 sixty-pound bags. Past that, ready-mix delivery saves your back and mixes more consistently. Order a little extra, since a short pour ruins the whole slab.
Thickness by job
Four inches handles patios, sheds, and walkways on firm, compacted ground. Use five to six inches for driveways and anything carrying vehicles, and add a gravel base and rebar or mesh for strength.
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Questions about this calculator
How many bags of concrete are in a cubic yard?
About 45 bags of 80 lb, 60 bags of 60 lb, or 90 bags of 40 lb make up one cubic yard.
How much concrete do I need for a 10x10 slab?
A 10 by 10 foot slab at 4 inches needs about 1.23 cubic yards, or roughly 62 bags of 60 lb concrete.
How thick should a concrete slab be?
Four inches is standard for patios, sheds, and walkways. Go to five or six inches for driveways or heavy loads, over a compacted base.
How many square feet does a bag of concrete cover?
An 80 lb bag covers about 1.8 square feet at 4 inches deep, a 60 lb bag about 1.35 square feet, and a 40 lb bag about 0.9 square feet.
Should I add extra concrete for waste?
Yes, order about 10 percent extra. A slab that comes up short cannot be patched invisibly, and uneven ground or spillage eats into the total.
Do I need rebar or mesh?
Add welded wire mesh or rebar for driveways, slabs over fill, or anything that will see heavy loads. Thin patios on stable ground can go without.