Fence Post Concrete Calculator
Bags of concrete per post hole, plus totals for the whole fence.
Enter your values
Enter the number of posts you are working with.
Enter the hole diameter in in.
Enter the hole depth in in.
Enter the post size (square) in in.
Choose one of: 50 lb (0.375 ft3), 80 lb (0.6 ft3).
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Bags per post
- 2
- Total bags
- 24
- Concrete per hole
- 1.09 cubic feet
- Total concrete
- 13.03 cubic feet (0.48 yd3)
Working
- 1hole 1.36 ft3 - post 0.28 ft3 = 1.09 ft3
Quick answer
Concrete per hole is the hole volume minus the buried post volume; divide by the yield of one bag to get bag count.
volume = pi x (hole/2)^2 x depth - post area x depth
At a glance
| What it does | Bags of concrete per post hole, plus totals for the whole fence. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Number of posts, Hole diameter, Hole depth, Post size (square), Bag size |
| Main output | Bags per post |
| Formula | volume = pi x (hole/2)^2 x depth - post area x depth |
| Cost | Free — no sign-up, no download |
How to use the Fence Post Concrete Calculator
- 1Count the posts and measure your hole diameter and depth.
- 2Hole diameter should be about 3x the post width; depth is a third of the post length or below frost line.
- 3Round up to whole bags per hole - part bags are hard to reuse once mixed.
Inputs explained
- Number of posts
- Enter the number of posts you are working with.
- Hole diameter(in)
- Enter the hole diameter in in.
- Hole depth(in)
- Enter the hole depth in in.
- Post size (square)(in)
- Enter the post size (square) in in.
- Bag size
- Choose one of: 50 lb (0.375 ft3), 80 lb (0.6 ft3).
Worked example
Using the values the calculator loads with:
Inputs
- Number of posts12
- Hole diameter10 in
- Hole depth30 in
- Post size (square)4 in
- Bag size80 lb (0.6 ft3)
Results
- Bags per post2
- Total bags24
- Concrete per hole1.09 cubic feet
- Total concrete13.03 cubic feet (0.48 yd3)
- hole 1.36 ft3 - post 0.28 ft3 = 1.09 ft3
Frequently asked questions
How deep should fence posts go?
One third of the above-ground height, and always below the local frost depth. For a 6 ft fence that usually means a 30 to 36 inch hole.
Can I pour dry concrete in the hole?
Yes for light fences: set the post, pour dry mix, then add water. For gates and windy sites, mix properly for full strength.
What do I need to enter into the Fence Post Concrete Calculator?
Just 5 values: number of posts, hole diameter, hole depth, post size (square), bag size. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Fence Post Concrete Calculator work out the answer?
Concrete per hole is the hole volume minus the buried post volume; divide by the yield of one bag to get bag count. It applies the formula volume = pi x (hole/2)^2 x depth - post area x depth and shows the working so you can check each step by hand.
Is the Fence Post Concrete Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.