Worked example
How Many 80 lb Bags of Concrete for a 10x10 Slab?
This example uses the 80 lb bag yield preset for a 10 ft by 10 ft slab, then lets you change thickness or bag yield.
Calculator inputs
Concrete Slab Calculator Results
Results update in your browser as you edit inputs. They are planning estimates, not complete shopping lists.
Enter project dimensions to calculate material quantity.
Inputs used in this example
- Slab size: 10 ft by 10 ft.
- Thickness: 4 inches.
- Bag yield preset: 80 lb bag at about 0.6 cubic feet.
- Waste factor: 5%.
Expected output
The calculator estimates about 33.33 cubic feet before waste, 35 cubic feet after waste, and about 59 bags when using a 0.6 cubic-foot bag yield.
When to adjust this example
- Use the actual yield printed on your 80 lb bag if it differs from the preset.
- Increase waste for uneven base preparation, overdig, or hand-mixing losses.
- Large projects may be better reviewed as ready-mix volume instead of individual bags.
Formula explanation
- Convert 4 inches to one-third of a foot.
- Multiply slab length, slab width, and thickness to get cubic feet.
- Apply the waste factor.
- Divide by 0.6 cubic feet per bag and round up.
Main calculator
Use the full Concrete Slab Calculator to change dimensions, waste factor, and optional user-entered unit price.
FAQ
Is every 80 lb concrete bag exactly 0.6 cubic feet?
No. The preset is a planning approximation. Use the yield printed on the specific bag when possible.
Does this calculate labor or delivery?
No. It estimates material quantity only and does not provide live prices, local quotes, or labor costs.