Fence Post Calculator: Posts, Hole Depth, Concrete and Pickets

About

A third of each post goes into the ground, never less than 2 feet, with 6 inches of gravel under it, so a 6 ft fence needs 10 ft posts in 3 ft holes. Lengths go in as feet and inches or metres. Below the calculator, draw the fence line around your lot to get its length and the corners. It is arithmetic from the usual rules, not an AI estimate.

01

Posts and spacing

Posts are set 8 feet on centre for standard 8 ft panels and rails, or 6 feet where the fence is tall, the wind is strong or the panels come in 6 ft lengths. The number of sections is the fence run divided by the spacing, rounded up, and the posts are one more than that; each gate adds a post. A 100 ft run with a 4 ft gate is 96 ft of fence, 12 sections at 8 ft, so 13 line posts plus 1 for the gate: 14 posts.

Use 4×4 posts for fences up to 6 ft and 6×6 for 8 ft fences, gate posts and windy sites. Pressure-treated lumber rated for ground contact, or cedar with a treated section below grade.

02

Hole depth, width and concrete

Bury a third of the post's total length, which works out to half the fence height above grade: 2 ft for a 4 ft fence, 3 ft for a 6 ft fence, 4 ft for 8 ft. Never less than 2 ft, and below the frost line where the ground freezes, which can mean 3 to 4 ft in northern states. Hole diameter is three times the post width, so 10 1/2 inches for a 4×4. Put 6 inches of gravel at the bottom for drainage, set the post, and fill with concrete to just above grade, sloped away from the post.

Concrete per hole is the hole volume minus the post. A 10 1/2 inch hole 3 ft deep around a 4×4 takes about 1.5 cu ft, which is two and a half 80 lb bags, so a 14 post fence needs around 35 bags. The calculator rounds up per fence, not per hole, and shows both 80 lb and 60 lb counts.

• 4 ft fence: 2 ft hole, 6 ft post, 2 rails.
• 6 ft fence: 3 ft hole, 10 ft post, 3 rails.
• 8 ft fence: 4 ft hole, 12 ft post, 3 or 4 rails, 6×6 posts.
• Gate posts: one size up, deeper, more concrete.

03

Rails and pickets

Two horizontal rails for fences up to 5 ft, three for 6 ft and taller, one per section each. Pickets are the fence run divided by the picket width plus the gap: a privacy fence with 5.5 inch pickets touching uses about 2.2 pickets per foot, so 210 for 96 ft; a picket fence with 3.5 inch gaps uses about 1.3 per foot. Board-on-board and shadowbox styles overlap the pickets and need up to twice as many.

04

Before you dig

Call 811 (in the US) to mark buried utilities, check the property line and the local height and setback rules, and ask the neighbour on a shared line. Draw the fence line on the canvas to measure each run and see the corners; the drawing is a schematic sketch for planning, not a survey, and nothing on this page is generated by an AI.