Concrete calculator
Concrete Calculator
Calculate concrete for rectangular slabs in cubic feet, cubic yards, and common bag sizes.
Results
- Base cubic feet
- 33.33 cu ft
- Base cubic yards
- 1.23 cu yd
- Cubic yards including waste
- 1.36 cu yd
- 40 lb bags
- 123
- 60 lb bags
- 82
- 80 lb bags
- 62
10% waste allowance
What this calculator does
This calculator estimates the concrete volume needed for rectangular slabs using length, width, thickness, quantity, and a selected waste allowance.
Formula used
Base cubic feet equals length in feet x width in feet x thickness in inches divided by 12 x quantity. Cubic yards equal cubic feet divided by 27.
How waste allowance works
Waste allowance increases the base volume before final volume and bag counts are shown.
Bag yield assumptions
Bag estimates use approximate yields of 0.30 cubic feet for 40 lb bags, 0.45 cubic feet for 60 lb bags, and 0.60 cubic feet for 80 lb bags.
Measurement reminder
Verify project measurements, site conditions, and supplier requirements before ordering concrete or bagged mix.