Calculators / Concrete
Concrete Calculator
To calculate concrete, enter the slab length, width, and thickness; this tool returns the volume in cubic yards, the number of 80 lb bags, and a cost estimate. One 80 lb bag yields about 0.6 cubic feet.
Real math, not AI guesses.
You need
1.3 cubic yards
Estimated cost
~$354
- Volume
- 33.3 cu ft
- With 5% waste
- 35 cu ft
- Cubic yards
- 1.3
- 80 lb bags (0.6 cu ft each)
- 59
Estimate only — actual quantities and prices vary by region and supplier. Verify with a professional before purchasing. Default price is a national average (as of 2026-06); edit it to match your supplier.
How to calculate concrete
The formula: cubic yards = (length × width × thickness⁄12) ÷ 27
- Measure the length and width in feet and the thickness in inches.
- Convert thickness to feet (inches ÷ 12), then multiply length × width × thickness for cubic feet.
- Divide cubic feet by 27 to get cubic yards.
- For bags, divide cubic feet by the bag yield (0.6 cu ft for an 80 lb bag) and round up.
Prices shown are national averages (as of 2026-06) and vary by region, brand, and supplier. They are estimates, not quotes.
Concrete FAQ
How many bags of concrete are in a cubic yard?+
A cubic yard is 27 cubic feet. An 80 lb bag yields about 0.6 cubic feet, so you need roughly 45 80 lb bags per cubic yard.
How thick should a concrete slab be?+
4 inches is standard for patios and walkways; 5–6 inches for driveways and areas with heavier loads.