Formula
How this estimate works
bags = cubic feet needed / selected bag yield, rounded up
An 80 lb bag is commonly estimated at about 0.60 cubic feet, so 24 cubic feet needs about 40 bags before waste.
How bag count is estimated
Bag count is based on the estimated cubic feet needed divided by the typical yield of the selected bag size. The result is rounded up because you cannot buy a fraction of a bag.
Bag yield varies by mix
Different brands and mixes can yield slightly different volumes. Use the bag label as the final reference when buying material.
Assumptions used
- Normal-weight concrete is estimated at 150 lb per cubic foot.
- Premix bag yield is estimated from common 40, 50, 60, and 80 lb bag sizes.
- Waste factor is applied after the base volume is calculated.
Before you order materials
- Check the exact yield printed on the bag.
- Make sure the total bag weight is practical to move and mix.
- Compare bag cost against ready-mix for larger pours.
Frequently asked questions
What concrete bag size should I choose?
80 lb bags are common for larger hand-mixed jobs, while 40 or 60 lb bags may be easier to lift.
Why is the bag count rounded up?
A partial bag cannot usually be purchased, and a small surplus is safer than running short mid-pour.
When are concrete bags not practical?
If the estimate reaches dozens of bags, ready-mix concrete may be faster and more consistent.