Calculate concrete volume for round post holes from hole count, diameter and depth. Get cubic feet, cubic yards and an approximate 80-lb bag quantity.
Enter your measurements and material details.
Actual holes are rarely perfect cylinders, so field-dug holes often need more material than the theoretical minimum.
Each post hole is treated as a cylinder. The radius is half the diameter, the circular area is π times radius squared, and volume is area times depth. That volume is multiplied by the number of holes.
Measure or specify the finished hole diameter and depth. If the post itself displaces a significant amount of concrete, this calculator conservatively does not subtract it.
Yes physically, but this planning calculator does not subtract the post, which provides a small allowance.
Only for simple round holes; engineered piers or bell footings need their actual geometry.
The result depends on hole diameter, depth and package yield.
Calculate the widened portion separately or increase the allowance.
No. Depth depends on structure, soil, frost and local requirements.
Using the example inputs shown in the calculator — Number of holes = 12, Hole diameter (in) = 12, Hole depth (ft) = 3, Extra allowance (%) = 10 — the result is 31.1 cubic feet. This demonstrates the formula with a complete set of numbers rather than a hidden assumption.
The result breakdown also shows Cubic yards: 1.152 yd³; 80-lb bags: 52. Replace the example values with field measurements and the exact product coverage, yield or package size you plan to buy.
For this post hole concrete calculator, the inputs with the greatest practical effect are number of holes, hole diameter and hole depth. Recalculate when any of those change; do not reuse a result from a different room, run, layer depth or product specification.
Post Hole Concrete Calculator is intended to help with quantity planning and arithmetic. It does not inspect the site, choose structural dimensions, determine code compliance or replace manufacturer installation instructions. Conditions such as slope, substrate quality, moisture, soil, framing, access and workmanship can change the final amount required.
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