Fence Post Hole Concrete Calculator
Estimate concrete volume and whole bags after subtracting the space occupied by a square fence post.
Check the source for the 0.375 cu ft sample yield and its limits. Use your own product label if it differs.
Use concrete depth, not total excavated depth
If a hole is 36 in deep and the bottom 6 in is gravel, enter 30 in for concrete fill. If concrete stops below grade, subtract that space too. Use your specified installation detail; this example is not a footing recommendation.
Why two bag counts?
For two holes needing 1.3 bags each, you need 3 bags if mixed concrete is distributed between holes, or 4 if you round each hole separately and discard the remainder. The tool reports both purchasing assumptions.
A checkable example
For one 12 in diameter hole, 30 in of concrete and a 3.5 in square post, net volume is approximately 1.751 cu ft before allowance. With 10% extra and 0.375 cu ft per bag, buy 6 bags. Use the yield printed on the specific product you buy.