Home and property
Concrete calculator
Enter the slab length and width in feet and the thickness in inches. Add extra for spills and uneven ground. Bag yield comes from the bag label.
What this means
- A 10 by 10 foot slab, 4 inches thick, needs about 1.36 cubic yards with 10% extra.
- With bags that yield 0.6 cubic feet each, that is 62 bags.
- Large pours are usually cheaper and easier as ready-mix delivered by the yard.
What if
About this calculator
What this calculator does
It finds the volume of a rectangular slab, adds a waste allowance, and converts it to cubic yards, cubic meters, and bags.
How it is calculated
cubic feet = length * width * (thickness / 12)
with waste = cubic feet * (1 + waste / 100)
cubic yards = cubic feet / 27
bags = cubic feet / yield per bag, rounded up
How to read the result
Order ready-mix in cubic yards. For small jobs, buy the bag count, rounded up to whole bags.
Sources and method
Standard arithmetic with no outside data. The formula is shown under How it is calculated, and unit tests check worked examples, including edge cases. Bag yields come from the manufacturer data sheet.
Questions
How many cubic feet are in a cubic yard?
27, because a yard is 3 feet and 3 * 3 * 3 = 27.
How thick should a slab be?
It depends on the use and local code. Ask a contractor or your building department.
Why add waste?
Ground is rarely flat and some concrete is lost. Running short mid-pour is worse than a little extra.
Where do I find bag yield?
On the bag. Yield depends on the bag size and mix.