How to Calculate Concrete for a Slab
A concrete slab is the simplest pour to calculate: length times width gives you area, multiply by thickness (in feet), divide by 27 to get cubic yards. The challenge is remembering to convert thickness from inches to feet before multiplying — 4 inches is 0.333 feet, not 4.
This calculator does the conversion for you. Enter thickness in inches directly. The results show cubic yards for ready-mix orders and bag counts for both 60 lb and 80 lb bags based on QUIKRETE's published yields.
Standard Slab Thicknesses
- Patio or walkway — 3 to 4 inches. Three inches is adequate for foot traffic only. Four inches is the standard for any patio that might see occasional vehicle access or heavy furniture.
- Driveway — 4 to 6 inches. Four inches for passenger cars. Six inches for driveways that will see pickup trucks, SUVs, or delivery vehicles regularly. Reinforcement with wire mesh or rebar is standard for all driveways.
- Garage floor — 4 to 6 inches. Four inches with reinforcement is the minimum code requirement in most jurisdictions. Six inches for a workshop or garage that will hold heavy equipment.
- Shed floor — 3 to 4 inches. Three inches is typically adequate for a residential shed storing lawn equipment and tools.
- Pool deck — 4 inches. Standard residential pool deck. Broom finish for slip resistance. Consider a fibrated mix to reduce cracking at expansion joints.
For structural slabs or foundations, consult your local building code and an engineer. The thicknesses above are guidelines for typical residential flatwork.
Need a different shape? The full Concrete Calculator covers slabs, footings, round columns, and post holes in one place.