Fence Post Calculator
Posts, sections, hole depth and concrete bags — from your fence length and spacing.
Posts needed
23
- Line posts
- 20 (19 sections)
- Corner, end & gate posts
- 3
- Actual spacing
- 7.89 ft on centre
- Post length to buy
- 8.0 ft
- Suggested set depth
- 24 in (frost line permitting)
- Concrete per post
- 1.17 ft³
- Concrete total (+10% waste)
- 29.5 ft³ · 1.09 yd³
- 80 lb bags
- 50 bags
- 60 lb bags
- 66 bags
- 50 lb bags
- 79 bags
- Gravel
- 6.0 ft³
Bag counts round up per size — buy one size, not all three. Check the frost line and any setback or property-line rules before digging.
Pricing the whole yard? Use the landscaping cost calculator →
How this is calculated
sections = ceil(fence length / spacing)
line posts = sections + 1
total posts = line posts + corners & ends + gates
hole area = π × (hole diameter / 2)²
concrete = (hole area − post area) × (depth − gravel)
× total posts × (1 + waste%)
bags = ceil(concrete ft³ / bag yield)Line posts are sections plus one because a run needs a post at both ends. Post area is subtracted from the hole because the post itself occupies part of it — a 6×6 displaces roughly twice what a 4×4 does. Bag yields are 0.60 ft³ for 80 lb, 0.45 ft³ for 60 lb and 0.375 ft³ for 50 lb of standard mix, and each size is rounded up independently so the three counts are alternatives rather than a shopping list.
Common spacing and depth
| Fence | Typical spacing | Minimum depth |
|---|---|---|
| 4 ft picket | 6-8 ft | 24 in |
| 6 ft privacy | 6-8 ft | 24-30 in |
| 8 ft privacy | 6 ft | 36 in |
| Chain link, residential | 8-10 ft | 24-30 in |
| Ranch rail, 3-rail | 8-10 ft | 24-30 in |
| Gate post, any fence | — | 36-48 in |
| Corner or end post | — | one size deeper |
Concrete per hole, 24 in deep
| Hole diameter | Cubic feet | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 8" | 0.53 | 1 | 2 |
| 10" | 0.92 | 2 | 3 |
| 12" | 1.40 | 3 | 4 |
| 16" | 2.62 | 5 | 6 |
Figures are for a 4×4 post with no gravel base and no waste allowance, computed with the same formula the calculator uses. They show why hole diameter matters more than post size: going from a 10 inch hole to a 16 inch hole nearly triples the concrete.
Frequently asked questions
How far apart should fence posts be?
Six to eight feet is the normal range, and eight feet is the most common because standard rails and panels are cut to that length. Go tighter to six feet for tall privacy fence, heavy panels or windy exposed sites, since spacing is what controls how much load each post carries.
How deep should a fence post be set?
A common rule is one third of the above-ground height, with a practical minimum of two feet, and always below the local frost line. A six foot fence therefore wants at least a two foot hole, and in northern climates the frost depth rather than the fence height sets the number.
How many bags of concrete per fence post?
A 4×4 post in a 12 inch hole set two feet deep takes roughly 2.5 to 3 bags of 80 lb mix. Bigger posts do not change this much because the hole diameter drives the volume far more than the post does — widening the hole by four inches costs more concrete than moving up a post size.
Should I use gravel under the post?
Yes in most soils. Four to six inches of compacted gravel under the post lets water drain away from the end grain instead of sitting against it, which is where wood posts rot first. It also reduces the concrete you need, since the gravel displaces it.
Do gate posts need to be bigger?
Usually. A gate hangs its full weight off one post and swings, so that post wants to be the next size up, set deeper — often 36 inches or more — and set in a wider hole. Undersized gate posts are the single most common fence failure, and they lean long before the rest of the line does.
Can I set posts without concrete?
You can tamp them in with compacted gravel, and for some soils and fence types that outlasts concrete because the post can dry out. Concrete is stronger against lateral load, which matters for gates, corners and tall privacy panels, so a common compromise is concrete at the corners and gates and gravel on the line posts.
Results are planning estimates and not professional engineering advice. Frost depth, soil type, wind exposure and local codes change what a post needs, and fences near property lines, easements or buried utilities carry legal requirements. Call your utility locate service before digging.