Fence Post Calculator
Work out how many posts a fence needs, how far apart to set them, and how deep and how long they should be. Enter the fence length, height, spacing, corners and gates. The example is a 6 ft privacy fence around three sides of a yard: 180 ft, with posts every 6 ft.
Safety: Post holes must reach below your local frost line where the ground freezes; check your local code for the required depth.
How to use the fence post calculator
- Enter the total fence length including gate openings, and the fence height above ground.
- Enter the post spacing: 6–8 ft for wood fences, or the panel width if you use prefab panels.
- Count the corners and extra ends: every place the fence turns, or stops and starts again, adds a post. Enter the gates too.
- Under Posts and concrete, enter the hole depth. The result shows the depth QUIKRETE's rule suggests for your height and the post length to buy.
How many fence posts do I need?
A straight fence has one more post than it has sections:
- Sections = fence length (minus gates) ÷ post spacing, rounded up
- Posts = sections + 1, + 1 for each corner or extra end, + 1 for each gate
Rounding up means the last section can be shorter than the rest; that's normal. A gate needs a post on each side, but one of those is already counted at the end of the fence run, so each gate adds one post.
Worked example: 180 ft of 6 ft fence, posts every 6 ft
This is the fence loaded above, with three corners and one 4 ft gate.
- Fence without the gate: 180 − 4 = 176 ft.
- Sections: 176 ÷ 6 = 29.3, rounded up to 30.
- Posts: 30 + 1 + 3 corners + 1 gate = 35 posts.
- Hole depth: for a 6 ft fence, QUIKRETE's ⅓ rule gives 36 in, so each post is 9 ft long; buy 10 ft posts.
- Concrete: 2.5 bags of 80 lb mix per post in 10 in holes, 89 bags in all.
At 8 ft spacing the same fence would need 22 sections and 27 posts: 8 fewer posts and holes, but longer, heavier rails between them.
How deep should fence posts be?
QUIKRETE's fence-post guidance is to bury about one third of the post's total length, in a hole about three times the post's width. Since a third of the post is underground, the depth works out to half the height above ground:
- 4 ft fence → 2 ft deep, 6 ft posts
- 6 ft fence → 3 ft deep, 9 ft posts (buy 10 ft)
- 8 ft fence → 4 ft deep, 12 ft posts
Where the ground freezes, the hole should also go below the frost line, or frost can lift the posts over a few winters. Local codes and HOAs may set their own depth and height rules, and you should always call 811 to have utilities marked before digging.
Fence post depth, length and concrete by fence height
| Fence height | Hole depth (⅓ of post) | Post length needed | Stock length to buy | Hole diameter 4×4 / 6×6 | 80 lb bags per 4×4 post |
|---|---|---|---|---|---|
| 3 ft | 18 in | 4.5 ft | 6 ft | 10.5 / 16.5 in | 1.2 |
| 4 ft | 24 in | 6 ft | 6 ft | 10.5 / 16.5 in | 1.5 |
| 5 ft | 30 in | 7.5 ft | 8 ft | 10.5 / 16.5 in | 1.9 |
| 6 ft | 36 in | 9 ft | 10 ft | 10.5 / 16.5 in | 2.3 |
| 8 ft | 48 in | 12 ft | 12 ft | 10.5 / 16.5 in | 3.1 |
QUIKRETE's rule: bury about one third of the post's total length, in a hole about 3× the post width. Go deeper where your frost line is lower, and follow local code. Bags assume a 10 in hole, no gravel, no waste.
Fence posts by length and spacing
| Fence length (straight run) | Posts at 6 ft spacing | Posts at 7 ft | Posts at 8 ft | Sections at 8 ft |
|---|---|---|---|---|
| 50 ft | 10 | 9 | 8 | 7 |
| 75 ft | 14 | 12 | 11 | 10 |
| 100 ft | 18 | 16 | 14 | 13 |
| 150 ft | 26 | 23 | 20 | 19 |
| 200 ft | 35 | 30 | 26 | 25 |
| 300 ft | 51 | 44 | 39 | 38 |
One straight run with no corners or gates. Add one post for each corner or extra end, and one for each gate.
Post-setting tips
- Set the corners and ends first. Stretch a string line between them, then mark the line posts along it at your spacing.
- Adjust the spacing to avoid a stub section. If the last section comes out very short, spread the difference over all sections instead.
- Gate posts take the most load. Many builders use a bigger post and a deeper, wider hole for gates.
- Panels set the spacing. With prefab panels, space posts at the panel width center to center, and set posts one at a time as you hang each panel.
- Check the property line. Confirm where your boundary is before setting the first post; a survey costs less than moving a fence.
Frequently asked questions
How many fence posts do I need?
Divide the fence length (minus gates) by the post spacing, round up, and add 1. Then add one post per corner or extra end and one per gate. A straight 100 ft fence at 8 ft spacing needs 14 posts.
How far apart should fence posts be?
6–8 ft is common for wood fences: 8 ft is standard, 6 ft makes a stiffer fence for tall or heavy designs and windy sites. For prefab panels, match the panel width.
How deep should a fence post be?
About one third of the post's total length (QUIKRETE), so half the height above ground: 3 ft deep for a 6 ft fence. Go below the frost line where that is deeper, and follow local code.
How long should fence posts be?
Fence height × 1.5 using the ⅓ rule: 9 ft for a 6 ft fence (buy 10 ft), 6 ft for a 4 ft fence, 12 ft for an 8 ft fence.
How wide should post holes be?
About three times the post width: roughly 10–12 in for a 4×4 (3.5 in) and 16–18 in for a 6×6 (5.5 in).
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