Construction & Materials
Post Hole Concrete Calculator
Use this post hole concrete calculator for fence, deck, mailbox, and small post-setting projects.
Concrete bags
—
- Concrete volume
- —
- Per hole
- —
Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
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What the post hole concrete calculator solves
Use this post hole concrete calculator for fence, deck, mailbox, and small post-setting projects.
Formula
How to use it
- Enter hole diameter, post diameter, and hole depth in inches.
- Enter number of posts.
- Round bag count up from total concrete volume.
How to read the answer
The post displaces part of the hole volume, so the calculator subtracts the post cylinder.
Common mistakes and edge cases
- Check frost depth and post requirements locally.
- Loose or belled holes use more concrete.
- Bag yield varies by mix size.
Worked examples
Fence posts
Concrete bags
18
Larger posts
Concrete bags
18
Frequently asked questions
Why subtract the post diameter?+
The post occupies space inside the hole, so that volume is not filled with concrete.
Does this decide hole depth?+
No. Soil, frost, wind load, and code requirements determine post depth.
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Last updated: May 15, 2026