How much concrete do fence posts need?
Estimate concrete around round or square posts from hole size, post displacement, count, and bag yield.
Short answer
Measure the holes and posts, calculate the space left around each post, multiply by the post count, and use the bag yield printed on the concrete product.
For homeowners checking a rough concrete material quantity after the post layout is known.
How to do it
Count matching posts
Group posts that use the same hole and post dimensions and enter that count.
Measure the hole
Enter hole diameter and depth, then choose the hole shape the tool supports.
Measure the post
Enter the round or square post size so its displacement is removed from the hole volume.
Use the bag yield
Enter the volume yield on the bag to get a whole-bag planning number.
Formula
Hole volume uses πr²h. Subtract post displacement, multiply by post count, add allowance, and divide by bag yield.
Illustrative 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.
Common mistakes
- Using post count from only the straight run
- Using bag weight instead of bag yield
- Treating the material estimate as a footing design
Before you buy
Check bag yield, water and mixing needs, bracing, delivery access, and the time required to pour the posts.
What this guide does not cover
Frost depth, soil, drainage, loads, reinforcement, hole shape, and local requirements need a separate footing review.
Use the calculator
Fence Post Concrete Calculator is the primary tool for this guide. You can also browse the other fencing calculators.