Formula
How this estimate works
cubic feet = pi x radius squared x hole depth x quantity
Eight 12 in diameter holes at 3 ft deep need about 0.77 cubic yards with 10% waste.
Round hole volume
Post holes are estimated as cylinders. The calculator converts diameter to radius, calculates circular area, then multiplies by hole depth and quantity.
Why hole diameter matters
A small increase in diameter increases volume across the entire depth of the hole. Measure the actual auger or dug hole size, not only the post size.
Assumptions used
- Normal-weight concrete is estimated at 150 lb per cubic foot.
- Premix bag yield is estimated from common 40, 50, 60, and 80 lb bag sizes.
- Waste factor is applied after the base volume is calculated.
Before you order materials
- Use actual hole diameter, not only post size.
- Account for over-digging and soil collapse.
- Follow product instructions for fast-setting mixes.
Frequently asked questions
How much concrete per fence post?
It depends on hole diameter and depth. A 12 inch diameter, 3 ft deep hole is much larger than a shallow small-diameter hole.
Should I add waste for post holes?
Yes. Soil collapse, uneven digging, and over-excavation can increase concrete use.
Can I use fast-setting concrete?
This calculator estimates volume. Follow the product label for water, placement, and curing instructions.