Post Hole Concrete Calculator

This works out how much concrete a set of post holes actually takes. Enter the hole diameter and depth, the post going into it, the depth of the gravel base and how many holes there are, and it returns the volume per hole and for the job, bag counts for 40, 50, 60 and 80 lb bags, and how much concrete the post and the gravel displace. A second action works the hole back from the post: the three-times-width diameter, how deep to bury a line post or a gate post, and the post length to buy. Treating the hole as a plain cylinder overstates a typical fence post by around a third, which is where the spare bags come from. It counts material only, and how deep a post has to go is a question for the frost depth and the local code.

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Measurements In
Hole, post and gravel dimensions are read in the smaller unit; post height above ground in the larger one. The bag sizes, auger sizes, post sizes and stock lengths offered are the ones sold in that market.

Enter the hole, the post that goes in it and the gravel under it. The post and the gravel both take up room the concrete does not have to fill, which is why this comes out below a plain cylinder of the same hole.

Three times the width of the post is the usual rule. 4 to 60 in, which is 102 to 1,524 mm.
6 to 144 in, which is 152 to 3,658 mm.
The nominal sizes are North American lumber; the metric sizes are the actual section a metric post is sold at. Both are offered whichever unit you chose, because the post in your hands is whatever it is.
Only used for the last two choices above, in the unit you chose. Measure the post, do not use the nominal size.
Set it to 0 if the post sits on the bottom of the hole. A blank box uses 6 in, or 150 mm.
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Measurements In
Hole, post and gravel dimensions are read in the smaller unit; post height above ground in the larger one. The bag sizes, auger sizes, post sizes and stock lengths offered are the ones sold in that market.

Work the hole back from the post. These are the rules of thumb the fence trade uses, not a code requirement: the depth that actually governs is the frost line and whatever the building department says.

A nominal 4x4 is 3.5 inches, a 6x6 is 5.5, a dressed 8x8 is 7.25. A metric post is 75, 100, 125 or 150 mm. 1 to 12 in, which is 25 to 305 mm.
In feet, or in metres on the metric setting. 1 to 20 ft, which is 0.3 to 6.1 m.
From the building department, in the smaller unit. Leave it at 0 if the ground does not freeze where you are.
A blank box uses 6 in, or 150 mm.
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