How to calculate fence materials
Everything on a fence keys off two numbers: total length and post spacing. Divide the length by the spacing to get sections, and posts are always one more than the number of sections — because a fence has a post on both ends.
sections = round up(length ÷ post spacing)
posts = sections + 1
rails = sections × rails per section
Worked example
A 150 ft fence with posts every 8 ft needs 150 ÷ 8 = 18.75, rounded up to 19 sections. That's 19 + 1 = 20 posts. With 3 rails per section that's 57 rails, and 2 bags of concrete per post is about 40 bags.
How much concrete per fence post?
Post holes should be about one-third the post's above-ground height deep. Concrete per post depends on hole size:
| Post / hole | Concrete per post |
|---|
| 4x4 post, standard hole | 1–2 bags (50 lb) |
| 6x6 post, larger hole | 2–3 bags (50 lb) |
| Gate / corner posts | 3+ bags (extra support) |
This calculator estimates 2 bags per post as a practical average. Frost-prone regions require deeper holes by code, which increases concrete.
Frequently asked questions
How many posts do I need for a 150 ft fence?
At standard 8-foot spacing, a 150-foot fence needs 20 posts — 19 sections plus one extra post to close the final end.
How far apart should fence posts be?
8 feet is the standard maximum for most wood and vinyl fences. Closer spacing like 6 feet adds strength for tall privacy fences or windy areas.
How many pickets do I need per foot?
For standard 5.5-inch pickets butted together, you need about 2.2 pickets per foot of fence. Spaced or shadowbox styles change this, so measure your gap.
How deep should fence post holes be?
Dig about one-third of the post's above-ground height, or roughly 2 feet for a 6-foot fence, and deeper than your local frost line where codes require it.