Wood Fence Calculator

With standard 8-ft post spacing, a wood fence needs one post per 8 linear feet plus one extra (sections + 1). For a 100-ft fence: ceil(100 ÷ 8) + 1 = 14 posts, plus any gate posts. Add 10% for waste and mis-set posts.

A 6-ft privacy fence typically uses 3 horizontal rails per section (top, middle, bottom) to prevent warping. For a 100-ft fence with 8-ft spacing, that is ceil(100 ÷ 8) × 3 = 39 rails. Each rail is an 8-ft 2×4.

4×4 posts are standard for residential wood privacy fences up to 6 ft tall. 6×6 posts are used for corner posts, gate posts, and 8-ft fences. Posts should be long enough for one-third burial below grade: a 6-ft fence typically uses 8-ft posts set about 2 ft deep, or 9-ft posts when frost-line rules require deeper burial.

The standard rule is one-third of the post length in the ground. For a 6-ft fence with 8-ft posts, that is about 2 ft deep. In frost climates, posts must extend at least 6 inches below the frost line regardless of the one-third rule, per IRC footing requirements—use taller posts when the frost-line depth exceeds the one-third burial. Check your local building code for specific requirements.

Yes. Any posts that contact soil should be pressure-treated lumber rated for ground contact (UC4B or higher for most residential applications, per AWPA Use Category guidelines). Rails and pickets do not need ground-contact rating but benefit from a weather-resistant species like cedar or treated pine.