Fence Post Calculator
Work out post count, hole depth and exactly how much concrete each fence post needs.
What you need
22
Posts needed
- Bags of concrete — whole job
- 47
- Bags per post
- 2.1
- Suggested minimum hole depth
- 24.00 in
- Cubic feet of concrete per post
- 1.0
- 0.5 cu ft bags of gravel
- 10
Rounded up across every hole.
Exact figure before rounding, so you can see the per-hole cost.
Estimates for planning. Confirm quantities with your supplier before ordering — see the assumptions below for the figures used.
How to use the fence post calculator
This is the post-specific companion to the fence calculator: how many posts, how deep the holes, and how many bags of concrete once you subtract the volume the post itself takes up. That last detail is why people run short.
What this calculator assumes
Every estimate depends on figures that vary by supplier and conditions. These are the ones used here, so you can sanity-check the result against your own quote.
- Concrete volume subtracts the post's own cross-section from the hole. Skipping that step is the most common reason people over-order by 20 to 30%.
- When the gravel base option is on, 5 inches of the hole depth is gravel rather than concrete.
- Bag yields are manufacturer figures: 0.30 cu ft for 40 lb, 0.375 for 50 lb, 0.45 for 60 lb and 0.60 for 80 lb.
- Suggested depth is a rule of thumb only — one third of exposed height, minimum 2 ft. Your local frost line and code govern the real minimum, and both override this figure.
- Corner, end and gate posts carry far more load than line posts and should be set deeper and wider than the calculation shows.
Frequently asked questions
How much concrete do I need for one fence post?
For a 4x4 post in a 10 inch hole 2½ feet deep, about 1.1 cubic feet after subtracting the post — roughly two and a half 60 lb bags. A 6x6 in a 12 inch hole 3 feet deep needs closer to 1.7 cubic feet, about four 60 lb bags.
How deep should a fence post be?
One third of the above-ground height as a minimum, so 2 feet for a 6 foot fence — but never shallower than your local frost line, which in cold regions can be 4 feet. Frost heave will lift a shallow post out of the ground over a few winters.
How wide should the post hole be?
About three times the post width, so 10 to 12 inches for a 4x4. Wider holes use much more concrete for little extra strength — depth does more than diameter. Gate posts are the exception and deserve both.
Should I put gravel under a fence post?
Yes, 4 to 6 inches of compacted gravel. It keeps the post end out of standing water, which is where rot starts, and gives the hole somewhere to drain. Set the post on the gravel and pour concrete around it — do not encase the bottom end.
Do I need to let the concrete cure before attaching rails?
Give it at least 24 to 48 hours with standard mix, or about 4 hours with a fast-setting product. Bracing the posts plumb while it cures matters more than the wait — concrete does not straighten a leaning post.
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