Fence post concrete calculator
Estimate outputs: Volume, Bags. Adjust Number of posts, Hole diameter, Hole depth to match your project.
Estimate outputs: Volume, Bags. Adjust Number of posts, Hole diameter, Hole depth to match your project.
Inputs and units
Use the units shown beside each field. Replace the sample values with your measurements and the figures on the selected product packaging.
| Parameter | Example input |
|---|---|
| Number of posts | 12 |
| Hole diameter | 30 cm |
| Hole depth | 80 cm |
| Post diameter | 10 cm |
| Volume yield per bag | 12 l |
| Waste allowance | 10 % |
Formula and assumptions
Volumeπ × max(0, (Hole diameter / 200)² - (Post diameter / 200)²) × Hole depth / 100 × Number of posts × (1 + Waste allowance / 100)
Bagsceil(Volume × 1000 / Volume yield per bag)
ceil = round up; floor = round down; max = the greater value. Trigonometric angles are converted from degrees to radians.
Allowance is applied before rounding to whole packages. Whole units are rounded up; displayed decimals are rounded only for readability.
Bulk density and compaction vary with moisture and the delivered material. The allowance does not model compaction; obtain the ordering conversion from your supplier.
Worked example
Sample values are examples, not product specifications. Run the calculation again with your own measurements.
| Result | Calculation |
|---|---|
| Volume | 0.6635 m³ |
| Bags | 56 |
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