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Calculation Machine

Fence Post Concrete Calculator

Bags of concrete per post hole, plus totals for the whole fence.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Bags per post
2
Total bags
24
Concrete per hole
1.09 cubic feet
Total concrete
13.03 cubic feet (0.48 yd3)

Working

  1. 1hole 1.36 ft3 - post 0.28 ft3 = 1.09 ft3

Quick answer

Concrete per hole is the hole volume minus the buried post volume; divide by the yield of one bag to get bag count.

The formula

volume = pi x (hole/2)^2 x depth - post area x depth

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Number of posts12
  • Hole diameter10 in
  • Hole depth30 in
  • Post size (square)4 in
  • Bag size80 lb (0.6 ft3)

Result

  • Bags per post2
  • Total bags24
  • Concrete per hole1.09 cubic feet
  • Total concrete13.03 cubic feet (0.48 yd3)

How to use the Fence Post Concrete Calculator

  1. 1Count the posts and measure your hole diameter and depth.
  2. 2Hole diameter should be about 3x the post width; depth is a third of the post length or below frost line.
  3. 3Round up to whole bags per hole - part bags are hard to reuse once mixed.

Frequently asked questions

How deep should fence posts go?

One third of the above-ground height, and always below the local frost depth. For a 6 ft fence that usually means a 30 to 36 inch hole.

Can I pour dry concrete in the hole?

Yes for light fences: set the post, pour dry mix, then add water. For gates and windy sites, mix properly for full strength.

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