Post Hole Calculator
Each hole is π r² h. Multiply by hole count and waste factor. Optional bag yield returns bag count. Default diameter unit is inches and depth unit is feet. Estimate only, not a permit, code check, or engineered design.
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How to estimate post hole concrete
- Enter hole diameter and pick its unit (inches by default).
- Enter hole depth and pick its unit (feet by default).
- Enter how many identical holes and a waste percent.
- Optionally enter bag yield in cubic feet per bag, then read volume and bags.
Post hole concrete volume
Cylinder holes with waste and bags
| One hole | π × r² × depth (feet) |
|---|---|
| Total ft³ | one hole × holes × (1 + waste/100) |
| Default diameter unit | Inches |
| Default depth unit | Feet |
| Bags | ceil(total ft³ / bagYield) when bagYield > 0 |
| Omitted | Bell bottoms, gravel base, and frost depth rules |
What this post hole volume covers
Identical cylindrical holes. Square footings and bell bottoms are out. Slab volume sits on concrete. Deck boards sit on deck flooring. Fence runs sit on fencing.
How volume and bags are computed
Diameter and depth convert to feet. one = π × (diameter/2)² × depth. total = one × holes × waste factor. When bagYield is greater than 0, bags round up from total ft³ divided by bagYield.
Frost depth, gravel, and sonotubes
Local frost lines set minimum depth. Gravel under the post is not subtracted here. Cardboard tube diameter should match the hole you type. Yard-scale fills sit on cubic yards.
Use cases
Four 12 in diameter by 3 ft deep holes at 10% waste with 0.6 ft³ bags. Comparing hole counts for a fence line. Not a stamped footing design.
Limits
No soil bearing check and no rebar cage. Estimate only, not a permit, code check, or engineered design. See the disclaimer.