Post Hole Concrete Calculator
Calculate the cylindrical hole, subtract the embedded post, multiply by the number of holes, and round concrete bags up.
- Concrete per hole
- 2.09 ft³ (0.08 yd³)
- Net concrete volume
- 20.94 ft³ (0.78 yd³)
- Order volume
- 23.04 ft³ (0.85 yd³)
- Rounding excess
- 0.36 ft³ (0.01 yd³)
Post displacement is subtracted. Enter the embedment filled with concrete; this does not choose hole depth or structural capacity.
Show calculation
π × hole diameter² ÷ 4 × depth − post displacement; × 10 holes; round bags upTransparent method and editable product assumptions. Verify current labels and project requirements.
How this calculator works
The hole is modeled as a cylinder at the diameter and concrete-filled depth you enter. Gravel bottoms or unfilled tops should be excluded from that depth.
The embedded post volume is subtracted over the same depth. A round post uses a cylinder; a square post uses side × side × depth. The net annular volume is multiplied by the whole number of holes.
Concrete waste is applied once, and finished yield converts volume to whole bags. This workflow intentionally does not choose hole diameter, embedment depth, footing capacity, frost depth, or fence design.
Formula
Net per hole = π × hole diameter² ÷ 4 × depth − post displacement; bags = ceil(total × (1 + waste) ÷ yield)The live substitution appears with your result.Control example: one 12-inch hole
A 12 in diameter × 36 in deep cylinder is 2.356 ft³ before displacement.
A 4 in round post displaces 0.262 ft³, leaving 2.094 ft³ of concrete per hole.
Assumptions and limits
- Holes are cylindrical and consistent.
- Post dimensions are actual embedded dimensions.
- The entire entered depth is concrete-filled.
- Bag yield is finished concrete volume from the label.
Common measuring mistakes
- Forgetting to subtract post displacement.
- Including a gravel bottom in concrete-filled depth.
- Using the calculator to choose structural hole dimensions.
Sources
Product-specific values remain editable. These sources support the method and stated examples; they are not a universal substitute for your supplier’s current label.
- QUIKRETE Concrete Mix 1101 data sheet Finished package yields for converting calculated volume to bags.
Questions people ask
Does the calculator subtract the post?
Yes. Select round or square and enter the actual diameter or side.
Should gravel depth be included?
No. Enter only the depth that will actually be filled with concrete.
Does this choose a safe hole depth?
No. Depth and diameter depend on loads, soil, climate, code, and the selected system.