Fence Calculator
Estimate posts, rails, pickets and bags of concrete for a wood fence from its length, height and post spacing.
How many fence posts do I need?
Posts = ⌈Fence length ÷ Post spacing⌉ + 1 + one per gate
A 100 ft fence with posts every 8 ft has 13 sections and 14 posts, plus one for a gate: 15 posts. A 6 ft privacy fence with 5.5 in pickets and no gaps needs 219 pickets and 39 rails (three per section).
Rails and pickets
Fences up to 4 ft tall use two horizontal rails per section; taller fences use three so the pickets do not warp in the middle. For a privacy fence, pickets are butted together; for a picket or spaced fence, enter the gap and the calculator divides the fence length by picket width plus gap.
How deep to set fence posts
The common rule is to bury one third of the post's total length, and never less than 24 in. Below the frost line is better in cold climates. A 6 ft fence therefore needs 8 to 8.5 ft posts. The calculator assumes a 10 in wide hole for a 4 × 4 post with 6 in of gravel at the bottom for drainage, then fills the rest with concrete.
| Concrete mix bag | Yield | Bags per post (6 ft fence) |
|---|---|---|
| 50 lb | 0.375 ft³ | about 2.5 |
| 80 lb | 0.6 ft³ | about 1.5 |
Check local rules before you dig: many cities limit fence height (often 6 ft in back yards and 3–4 ft in front), require a permit, or set a minimum distance from the property line. Call 811 to have buried utility lines marked for free.
Frequently asked questions
How far apart should fence posts be?
Usually 8 ft apart for wood fences; 6 ft for heavy materials or windy sites. Vinyl and metal panels come in fixed widths, so follow the panel length.
How many bags of concrete per fence post?
For a 4×4 post in a 10 in hole about 2 ft deep, roughly two to three 50 lb bags or one to two 80 lb bags.
How many pickets do I need for 100 feet of fence?
With standard 5.5 in pickets and no gaps, about 219 pickets.
Last reviewed October 2026. Results are estimates; check important decisions with a qualified professional.