Concrete Calculator
Calculate the concrete you need for a slab, patio, or footing — in cubic yards and the number of bags.
Concrete Calculator
Calculate cubic yards and the number of bags for a slab, pad, or footing.
4 inches is typical for a patio or walkway slab.
You'll need
0 cubic yards
Enter dimensions to calculate
How to calculate concrete
- Measure the length and width of the slab in feet.
- Choose a thickness — 4 inches is typical for patios and walkways.
- Volume = length × width × thickness (in feet).
- Divide by 27 for cubic yards, then convert to bags based on bag yield.
How many bags of concrete in a cubic yard?
It depends on bag size. An 80 lb bag yields about 0.6 cubic feet, so a cubic yard (27 cubic feet) takes about 45 of them. A 60 lb bag takes about 60 bags per yard, and a 40 lb bag about 90. For anything above roughly half a cubic yard, ready-mix delivery is usually easier and cheaper than mixing bags by hand.
Frequently asked questions
How thick should a concrete slab be?
4 inches is standard for patios, walkways, and shed bases. Driveways and areas holding heavy vehicles usually need 5–6 inches with reinforcement. Always check local codes for structural work.
Should I order extra concrete?
Yes. This calculator adds about 5% for spillage and uneven subgrade. For ready-mix delivery, many people round up to the next quarter yard, since running short mid-pour is a serious problem.
Bags or ready-mix?
Bags suit small jobs like post footings or a small pad. For larger slabs, mixing dozens of bags by hand is exhausting and inconsistent — ready-mix delivered by truck is the practical choice.