Formula
Hole volume uses πr²h. Subtract round or square post displacement, multiply by post count, add allowance, then divide by bag yield.
Fence Post Concrete Calculator
Estimate concrete around round or square posts, subtract displacement, and round to whole bags.
How this fence post concrete estimate works
Concrete quantity depends on both the hole and the post. Entering the post size makes the displacement visible instead of treating every hole as solid concrete.
Worked example
For a 12 inch diameter, 30 inch deep hole, a 4 inch round post displaces part of the hole volume. Repeat that net volume for every post before bag rounding.
Before you buy
Use the yield printed on the concrete bag, not the bag weight alone. Have a plan for water, mixing, bracing, and the time required for a multi-post pour.
Assumptions
Defaults are starting points. Replace coverage, density, package yield, spacing, and allowance values with the product or plan you are actually using.
Limitations
This is a material estimate, not a footing design. Frost depth, soil, drainage, post loads, reinforcement, and local requirements may change the installation.