Concrete Calculator
Size a pour and see how many bags you need.
Your numbers
%
Your results
Volume (cu ft)
Volume (cu ft)
—
Volume (cu yd)
—
Bags needed
—
Volume (cu m)
—
Concrete Calculator by TheCalcTools
How the Concrete Calculator works
Enter the slab dimensions and thickness.
Volume is length × width × thickness, plus an allowance for waste and uneven subgrade.
Bag counts use the typical yield of premixed concrete.
The formula
Volume (cu ft) = length × width × thickness (ft)1 cubic yard = 27 cubic feet
Worked example
Using the default values shown in the calculator:
| Length (ft) | 10 |
|---|---|
| Width (ft) | 10 |
| Thickness (in) | 4 |
| Bag size | 80 lb bag (0.6 cu ft) |
| Extra for spillage | 10 % |
- 10 × 10 × 4/12 ft = 33.3 cu ft; with 10% extra = 36.7 cu ft (1.36 cu yd).
- That is 62 bags of 80 lb.
Result:
| Volume (cu ft) | 36.7 |
|---|---|
| Volume (cu yd) | 1.36 |
| Bags needed | 62 |
| Volume (cu m) | 1.04 |
Frequently asked questions
What thickness should a patio slab be?
4 inches is typical for patios and walkways. Driveways and garage floors are usually thicker. Check local building codes.
Should I order ready-mix?
Over about 1 cubic yard, ready-mix delivery is usually easier than mixing dozens of bags.
Sources and further reading
Related calculators
More in Construction & DIY · All calculators
This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.