Post-Hole Concrete Calculator
Estimate concrete volume, bag quantity, excavation volume and material cost for round fence, deck or sign-post holes.
Default project preview
47 bags
Concrete volume
1.02 yd³
Concrete per hole
2.3 ft³
Excavated volume
1.05 yd³
Total drilled depth
36 ft
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Number of post holes
Enter this project assumption in a unitless value. The current imperial default is 12. Minimum: 1.
Hole diameter
Enter this project assumption in in. The current imperial default is 12 in.
Hole depth
Enter this project assumption in ft. The current imperial default is 3 ft.
Post diameter or width
Enter this project assumption in in. The current imperial default is 4 in. Minimum: 0.
Extra allowance
Enter this project assumption in %. The current imperial default is 10 %. Minimum: 0. Maximum: 50.
Concrete yield per bag
Enter this project assumption in ft³. The current imperial default is 0.6 ft³.
Price per bag
Enter this project assumption in a unitless value. The current imperial default is 6.25. Minimum: 0.
Ready-mix price
Enter this project assumption in per yd³. The current imperial default is 170 per yd³. Minimum: 0.
How to read the outputs
Concrete volume
allowance included. Default preview: 1.02 yd³.
Concrete per hole
average filled annulus. Default preview: 2.3 ft³.
Excavated volume
full hole volume. Default preview: 1.05 yd³.
Total drilled depth
all holes combined. Default preview: 36 ft.
Bagged cost
rounded full bags. Default preview: $293.75.
Ready-mix cost
volume only. Default preview: $174.07.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Concrete per hole = cylindrical hole volume − post displacement. Total order = concrete per hole × hole count × allowance.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 29, 2026
Use this calculator to estimate concrete for cylindrical post holes after accounting for the post displacement. It is useful for fence, deck and sign-post ordering, but hole depth, diameter, frost protection and post design remain project-specific.
Calculation steps
- 1Calculate each cylindrical hole volume.
- 2Subtract the portion occupied by the post.
- 3Multiply by the number of holes.
- 4Add placement allowance and round up to full bags or delivery units.
Worked numerical example
Twenty holes 12 in in diameter and 36 in deep around 4 in square posts require roughly 47.1 ft³ of concrete after subtracting the posts. At 0.6 ft³ per bag with 10% allowance, order about 87 bags.
Purchasing and rounding
Bag yields vary with package weight and water content. For many large holes, compare bag handling with a small ready-mix delivery and minimum-load charges.
Interpret the result
A surprisingly high quantity often comes from deep or oversized holes. Increasing diameter has a squared effect on volume.
Page-specific assumptions
- Straight cylindrical holes.
- Posts are centered and extend through the concrete depth.
- No bell-shaped footing unless included separately.
- Published bag yield is accurate.
Common mistakes
- Using hole diameter as radius.
- Failing to subtract the post.
- Ignoring loose soil enlargement.
- Selecting hole dimensions from the calculator rather than project requirements.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Post-Hole Concrete Calculator questions
Should the post volume be subtracted?+
Yes for a closer estimate. The calculator subtracts a circular displacement based on the entered post width.
How deep should a post hole be?+
Depth depends on post height, wind, soil, frost line and local requirements.
Can dry concrete be poured directly into the hole?+
Follow the exact product instructions and project requirements; installation methods vary.