Post Hole Concrete Calculator
By Vinod Kondeti · Updated
Setting fence or deck posts? The concrete fills the hole minus the space the post takes up. This calculator subtracts a square post from a round hole, so the bag count is not inflated.
How do I measure for a post hole pour?
- A nominal 4×4 post is about 3.5 in square and a 6×6 is about 5.5 in. Enter the actual size.
- Enter the full hole depth. If you put gravel in the bottom, subtract that depth first.
- The per-hole bag count is easier to plan if you set the number of holes to 1.
Post hole concrete questions
How many 50 or 80 lb bags for one 10 in × 30 in hole with a 4×4?
About 1.15 ft³ of concrete, which is 2 bags of 80 lb mix (0.60 ft³ each) or 3 bags of 60 lb.
Is the post subtracted the full depth?
Yes. The tool assumes the post sits in the concrete for the whole hole depth, which is the usual way to set one.
Bag yields: 0.30 / 0.45 / 0.60 ft³ for 40 / 60 / 80 lb standard concrete mix (manufacturer data sheets). The concrete guide has the formulas and worked examples.
Sources
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