How to use this calculator
- Choose dimensions or known volume as the input method.
- Enter project measurements or a known volume.
- Select 40 lb, 60 lb, or 80 lb bags.
- Set a waste allowance and calculate the whole-bag purchase quantity.
How the calculation works
The calculator converts the project to cubic feet, applies the selected waste allowance, divides by the nominal yield for the selected bag weight, and rounds up to the next whole bag.
Formula
Adjusted volume = project volume × (1 + waste % ÷ 100) Bags = adjusted cubic feet ÷ bag yield, rounded up Nominal yields: 40 lb = 0.30 ft³; 60 lb = 0.45 ft³; 80 lb = 0.60 ft³
Worked example
A project requiring 10 cubic feet with 10% waste has an adjusted volume of 11 cubic feet. At a nominal 0.60 cubic feet per 80 lb bag, 18.34 bags are calculated, so 19 whole bags are required.
Project considerations
- Bag yields are planning assumptions, not guarantees.
- Check the manufacturer’s current yield and water instructions.
- Whole-bag quantities are always rounded upward.
Frequently asked questions
Why do bag yields differ by weight?
Larger bags contain more dry mix and normally produce more cured volume. This calculator states the nominal yield used for each size.
Can I enter a volume I calculated elsewhere?
Yes. Choose known volume and enter cubic feet, cubic yards, or cubic meters.