Fence Post Size Calculator

The widely used rule of thumb is to bury one-third of the post's above-ground height, with a hard minimum of 24 inches regardless of fence height. So a 6 ft fence needs at least 24 in of burial (8 ft post total), and an 8 ft fence needs about 32 in. In cold climates, go below your local frost line plus a 3 in buffer — whichever is deeper.

It depends on hole size, not the post. A common 4x4 post in a 10 in diameter x 36 in deep hole with a 6 in gravel base needs about 1.15 cu ft of concrete after subtracting the gravel and the post itself — that's 2 bags of 80 lb mix (1.92 bags), 3 bags of 60 lb, or 4 bags of 50 lb. This calculator computes it from your actual hole diameter and depth.

The hole should be at least 3 times the width of the post. For a 4x4 (3.5 in actual), that means roughly 10-12 in; for a 6x6 (5.5 in actual), 12 in is standard practice for a fence. Deeper or wind-exposed fences go wider. Gate and corner posts get an oversized hole.

Use 4x4 for line posts on fences up to 6 ft tall in normal wind. Step up to 6x6 for corner, end, and gate posts, any fence taller than 6 ft, or high-wind exposure. 6x6 posts are roughly 6x stiffer in bending than 4x4 and resist the leverage of a swinging gate. This is a simplified planning guide, not structural engineering.

Yes, where the ground freezes. Frost heave can lift posts out of the ground as saturated soil freezes and expands. Set the bottom of the post at least 3 in below your local frost line — the tool takes the deeper of the 1/3 rule and the frost-line depth automatically.

Gate posts carry a swinging, dynamic load, so set them 6 in deeper than your line posts and use a wider hole. 6x6 posts are recommended for gates. The calculator applies the +6 in gate bonus automatically in post-schedule mode.

Common spacing: wood privacy 6-8 ft, vinyl panels 6 or 8 ft (match the panel width), chain link 10 ft, ranch rail / farm fence 8-12 ft, and electric fence 20-30 ft with step-in posts. Wider spacing saves posts but needs heavier rails or more wire tension.

An H-brace is a corner/end assembly for wire and farm fences: two vertical posts (min 5 in diameter, set 3 ft deep) joined by a horizontal 8 ft rail (min 4 in diameter), with a diagonal tension wire. Per USDA NRCS guidance, use a single H-brace for straight spans up to 165 ft and double H-braces at all corners, fence ends, and gate openings, with pull assemblies every 660 ft on long runs.

Yes for light-duty farm and rail fences — tamped soil or compacted gravel works and drains better. Use concrete for privacy fences, gates, corner posts, and windy or soft-soil sites. Always put 6 in of gravel under the post for drainage to slow rot.

Post length = fence height + burial depth, then round up to the nearest stock length (6, 8, 10, or 12 ft). Example: a 6 ft fence buried 24 in needs 8 ft of post — an 8 ft stock post. A 6 ft fence in a 36 in frost zone needs 9 ft, so buy a 10 ft post.