Bags of Concrete Calculator
Find how many 40, 50, 60, 80 or 90 lb bags of concrete mix you need for fence and deck post holes, small slabs, or any volume.
- Per hole
- Total volume
- Other bag sizes
- Weight to haul
- Cost
- Add a price to estimate
Job List
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| Job | Details | Cubic Feet | Bags | Cost | Remove |
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How Many Bags of Concrete Do You Need?
Find the volume to fill in cubic feet, then divide by the yield of one bag. Quikrete's data sheet lists these yields for its concrete mix: a 40 lb bag makes 0.30 cubic feet, 50 lb 0.375, 60 lb 0.45, 80 lb 0.60 and 90 lb 0.675. Round up, since you can't buy part of a bag.
For a post hole, the concrete fills the hole around the post, so subtract the post's volume from the hole's.
Sizes are in inches; dividing by 1,728 turns cubic inches into cubic feet. The concrete depth is the hole depth minus any gravel in the bottom.
Worked Example
80 Lb. Bags per Post Hole
For a 4×4 post, no gravel, no waste.
| Hole | 24″ Deep | 30″ Deep | 36″ Deep | 42″ Deep |
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Tips for Setting Posts
A common rule of thumb is a hole about three times the post's width and a third to a half of its above-ground height deep, and below the frost line where the ground freezes. A few inches of gravel in the bottom helps drainage and saves concrete. Slope the top of the concrete away from the post so water runs off. Check local code for decks and other structures.