Category: Calculators
Concrete Calculator
Work out the concrete volume for a slab or footing
Enter the length, width and thickness of a slab or footing to estimate the concrete volume needed, and optionally the number of bags.
Length, width and thickness must all use the same unit; the volume is in that unit cubed. Bag count only appears once a bag yield above zero is entered, in the same cubic unit.
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What this tool does
The calculator multiplies length by width by thickness to get the volume, then adds your waste percentage for spillage and an uneven subgrade. If you also enter the volume one bag yields, the calculator divides the total volume by that yield and rounds up to the number of bags.
How to use it
- Enter the length, width and thickness in one consistent unit.
- Enter a waste percentage for spillage and an uneven base.
- Optionally enter the volume yield printed on your bag.
- Read the volume needed, and the bags if you entered a yield.
Privacy
This tool runs entirely in your browser. Your input is never uploaded, stored or shared — closing the tab removes it.
Frequently asked questions
- What unit should thickness be in?
- The same unit as length and width; if you enter length and width in meters, enter thickness in meters too, such as 0.1 for a 10 cm slab, and the volume comes out in cubic meters.
- Where do I find a bag's volume yield?
- Bagged concrete mix states a yield, such as '0.017 cubic meters' or '0.6 cubic feet' per bag; enter that figure in the same cubic unit as the volume result.
- What waste percentage is typical?
- 5 to 10% is common for a straightforward slab or footing to cover spillage and an uneven subgrade; irregular shapes or hand mixing often warrant a higher figure.