Concrete Calculator
Use your own numbers after reviewing the example below.
Quick answer
Larger bags generally produce more mixed concrete per bag, so the number of bags needed falls as bag size rises. Use the yield printed on the specific product for the purchase calculation.
Formula or method
Step-by-step
- Calculate required cubic feet including any extra allowance.
- Choose the bag size and find its stated mixed yield.
- Divide total cubic feet by the stated yield.
- Round up to a whole bag.
Worked example
For a planning volume of 6 ft³, approximate yields of 0.30, 0.45 and 0.60 ft³ imply about 20 forty-pound bags, 14 sixty-pound bags, or 10 eighty-pound bags.
How to interpret the result
The values are useful for comparing bag quantities, but actual yield can differ by product and water content. Check the bag label.
Common mistakes
- Assuming every brand has identical yield.
- Comparing bag weights without comparing mixed yield.
- Ignoring the physical handling difference between bag sizes.
Frequently asked questions
Which bag size needs the fewest bags?
An 80 lb bag generally requires fewer bags for the same volume because each bag yields more mixed concrete.
Are the yields exact?
No. They are planning approximations; use the manufacturer label for purchasing.
Can I use cubic yards?
Yes. Convert cubic yards to cubic feet by multiplying by 27, then divide by bag yield.