Concrete & masonry
Post Hole Concrete Calculator
Enter the hole diameter, depth and number of holes to estimate concrete for fence posts or other round post holes. You can also subtract the post and a gravel base.
YOUR MATERIAL ESTIMATE
A clearer quantity starts here.
Enter your measurements, check the units and calculate. Your result will include the assumptions and rounding steps.
Show calculation
THE WORKFLOW
How to use this post hole concrete calculator
- Enter hole diameter, depth and number of holes; confirm the units.
- Optionally select a post shape and size to subtract displacement, and enter gravel base depth.
- Check bag yield, add optional waste and calculate per-hole and total concrete volume.
Formula & assumptions
Per-hole concrete = (hole cross-sectional area − post cross-sectional area) × (hole depth − gravel base depth). Total = per-hole × number of holes.
Round holes, centered round or square posts and constant cross-sections are assumed. Post displacement spans the concrete depth. Gravel depth is optional and user-entered. No dimensions or frost depths are selected by the tool.
See methodology and sources →AN ARITHMETIC EXAMPLE, NOT A RECOMMENDATION
Worked example
Example only: one round hole, 12 in diameter and 24 in deep, without displacement or extra. These dimensions are not guidance.
- Concrete per hole, net1.571 ft³
- Net volume0.058 yd³
- Order volume0.058 yd³
- Order volume1.571 ft³
Example calculation
Bags: 1.570796 ft³ ÷ 0.6 ft³ per bag = 2.617994; round up to 3.
Hole area π × (0.3048 / 2)²; subtract no post. Concrete depth 0.6096 m. Per hole = 0.04448 m³; × 1 holes = 0.04448 m³; apply 0% extra.
Common questions
Does this determine hole depth?
No. Supply the dimensions specified for your own project. The tool does not determine post embedment or frost depth.
How is a post subtracted?
Its entered cross-sectional area is subtracted over the concrete depth. A square post is checked by its diagonal to ensure it fits in the round hole.
Estimates only. Verify measurements and manufacturer packaging/yields. Project conditions vary. This tool does not provide structural engineering advice. Read the disclaimer.