Estimate concrete around round or square posts, subtract displacement, and round to whole bags.
Use this calculator for a rough concrete quantity around fence posts. It shows the hole volume and subtracts the post displacement, so the estimate is tied to the dimensions you enter rather than assuming every hole is solid concrete.
The tool calculates hole volume with πr²h, subtracts the post displacement, multiplies by post count, adds the allowance, and divides by bag yield.
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.
Use the yield printed on the bag, not the bag weight alone. Plan for water, mixing, bracing, and the time needed to pour a group of posts.
Hole shape, post shape, soil, frost depth, drainage, post loads, reinforcement, bag yield, and local requirements can change the real concrete need.
This is a material estimate, not a footing design. It does not choose frost depth, reinforcement, drainage, post loads, or local requirements.
The post occupies part of the hole. Subtracting that space gives a more useful material estimate than treating the full hole as concrete.
No. Use the volume yield printed on the bag. Weight and yield are different product details.
No. It only estimates concrete from the dimensions you enter. Frost, soil, loads, drainage, and local requirements need a separate review.
Short, practical help for the next step in this project.