Concrete Calculator
Cubic yards and bags for slabs, footings and posts.
Reviewed by James Whitfield · How we check our maths
Your values
ⓘ Live results
Results
- Concrete needed
- 2.72 cubic yards
- Cubic feet
- 73.3
- 80 lb bags
- 123
- 60 lb bags
- 163
- Approximate weight
- 11,000 lb
Quick answer
Concrete volume is length × width × thickness converted to cubic yards; one 80 lb bag yields 0.6 cubic feet.
The formula
Cubic yards = L × W × T(ft) ÷ 27
Worked example
Worked example
Using the values the calculator loads with.
Inputs
- Length20 ft
- Width10 ft
- Thickness4 in
- Waste allowance10 %
Result
- Concrete needed2.72 cubic yards
- Cubic feet73.3
- 80 lb bags123
- 60 lb bags163
- Approximate weight11,000 lb
How to use the Concrete Calculator
- 1Measure the length and width of the pour.
- 2Enter thickness in inches.
- 3Read cubic yards and bag counts.
Frequently asked questions
When should I order ready-mix?
Above about one cubic yard. Mixing 45 bags by hand is slow enough that cold joints form between batches.
How thick should a slab be?
4 inches for patios and walkways, 5–6 inches with rebar for driveways carrying vehicles.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error