Post holes 1
Number of holes: — qty · Hole diameter: — in · Depth: — ft · Post diameter: — in
Fence and deck post planner
Post Hole Concrete Calculator
Calculate concrete for fence and deck post holes, including optional post displacement.
Project
Subtract the post only if concrete will not fill the hole
Formula
Hole cylinder minus the post, times the count
Hole volume = count × π × (hole radius² − post radius²) × depth. Leave post diameter blank when the hole will be filled solid. Depth is entered in feet; diameters are entered in inches.
Common mistake
Typing the post width into the hole field
An 8-inch hole around a 4-inch post is not an 8-inch post. The hole diameter sets the concrete cylinder. The post diameter only subtracts the wood or steel that occupies part of that hole.
Worked quantities
Fence and deck holes
Identical holes are counted together. A corner, gate, or deck pier with a different diameter or depth needs its own section rather than an average hole.
| Holes | Post subtracted | Measured yd³ | 80 lb bags |
|---|---|---|---|
| 8 holes, 8 in × 2 ft | No | 0.21 | 11 |
| 12 holes, 8 in × 2 ft, 4 in posts | 4 in post | 0.23 | 12 |
| 10 holes, 10 in × 2.5 ft | No | 0.51 | 25 |
| 6 holes, 12 in × 3 ft, 4 in posts | 4 in post | 0.47 | 24 |
| 4 holes, 18 in × 4 ft, 6 in posts | 6 in post | 0.93 | 47 |
Field check
Use hole diameter, not post width
The required cylinder starts with the actual hole diameter and depth. Enter post diameter only when you deliberately want the estimator to subtract the post volume from the hole.
Field check
Group holes with the same geometry
Count identical holes together. If corner posts, gate posts, or deck piers have different diameters or depths, add another section instead of using one average hole.
Field check
Depth is a project input
The calculator does not choose embedment, footing depth, frost protection, or structural capacity. Use the dimensions required by the project and applicable local rules, then calculate the material quantity.
Questions
What the post-hole calculator answers
Should I enter hole or post diameter?
Hole diameter is required. Post diameter is optional and only controls displacement.
Can I leave post diameter blank?
Yes. ConcreteQty then assumes the full hole is filled with concrete.
Does this choose the correct hole depth?
No. Depth must follow your project requirements and local rules.
Next step
Switch to tubes or columns if the hole is formed
Bag yields follow the cited manufacturer data. See sources and review dates.