Use a few spot sizes for an odd hole.
⚙️Calculation Parameters
📊Calculated Output
How Irregular Post Hole Calculator Works?
To estimate a ragged hole, the Irregular Post Hole Calculator splits the hole into short sections, measures each diameter and adds the section volumes. The process takes 4 steps.
Split the depth
Divide the hole into sections of 6 in to 12 in (15 cm to 30 cm).
Measure each width
Measure the diameter at the middle of each section. Measure 2 directions and average them, if the hole is oval.
Sum the sections
The calculator finds each section cylinder and adds them.
Compare with nominal
The tool compares the measured total with the auger size, so the over-dig is clear.
Irregular Post Hole Calculator Formula
The Irregular Post Hole Calculator uses stacked sections.
Section volume
Vᵢ = π × (Dᵢ ÷ 24)² × (hᵢ ÷ 12)Dᵢ is the section diameter.
Hole volume
V = Σ VᵢSum of sections.
Oval average
D = (D_a + D_b) ÷ 2Average of 2 perpendicular widths.
Worked example: 4 sections of 12 in, widths 14, 12, 11 and 13 in
- 1.069 + 0.785 + 0.660 + 0.922 = 3.436 ft³
- Nominal 12 in auger = 3.142 ft³
- Over-dig = 9.4%
Irregular Post Hole Calculator Conversion Table
The irregular hole conversion table shows a 48 in (122 cm) hole measured in 4 sections, with the average-diameter shortcut and the nominal auger volume.
| Section diameter | Section height | ft³ |
|---|---|---|
| 14 in | 12 in | 1.069 |
| 12 in | 12 in | 0.785 |
| 11 in | 12 in | 0.660 |
| 13 in | 12 in | 0.922 |
| Average 12.5 in | 48 in | 3.409 |
| Section total | 48 in | 3.436 |
| Nominal 12 in | 48 in | 3.142 |
Short sections give a closer estimate in holes with rocks or caving walls.
What is Irregular Post Hole Calculator?
An Irregular Post Hole Calculator is an estimating tool that measures uneven holes in sections and adds the section volumes.
Unformed holes are rarely straight. Rocks pull out, sand caves and augers wobble. A hole dug with a 12 in auger can measure 11 in to 14 in across at different depths. The section method follows those changes and gives a closer volume than the auger size.
The calculator suits holes poured without a tube, or holes where the concrete fills the gap around a tube.
What are the uses of Irregular Post Hole Calculator?
There are 4 main uses of the Irregular Post Hole Calculator.
Rocky soil
Crews measure holes that widened around removed rocks.
Sandy soil
Installers measure holes with caving walls.
Hand-dug holes
Owners measure post-hole digger holes.
Unformed pours
Builders pour concrete straight into the earth hole.
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