How far apart: 6, 8 or 10 feet

8 ft on center is the default for wood privacy fences: strong enough for pickets, rails and normal wind, and economical on posts. Go 6 ft in exposed windy areas, on slopes, or for tall 8-ft fences. 10 ft only works for light ranch rail or temporary mesh — pickets sag and rails flex at that span.

Spacing is measured between post centers, so a 100-ft line at 8-ft spacing has 12.5 spans — you can't cut a span in half, which is why the count always rounds up.

Counting posts for a run

Posts = (length ÷ spacing) rounded up, plus 1 for the end post, then add every corner, gate post and change of direction. A simple 100-ft straight line: 100 ÷ 8 = 12.5 → 13 spans → 13 posts. Add a corner at either end and you're at 15.

Gate openings each need two posts (one each side), set deeper and stouter than line posts.

Hole depth and the frost line

Dig the hole about one-third of the post height above ground. A 6-ft post gets an 18–24-in hole; an 8-ft post gets 24–30 in. In cold climates the hole must also reach below the frost line — anywhere from 12 in in the South to 48+ in the far North — or frost heave will push the post up every winter.

Add 2–4 in of gravel at the bottom for drainage so the post bottom doesn't sit in water. The hole should be 3× the post width (an 8-in diameter for 4×4 posts).

Concrete per post

A standard 6-ft post in an 8-in × 24-in hole takes 2–3 bags of 50-lb fast-setting concrete. Multiply by your post count and add spares: 13 posts × 2.5 = about 33 bags — buy 35–36 to cover spillage and low spots.

Fast-setting mix is worth the small premium for fences — you can set and brace posts the same afternoon instead of waiting on a slow cure.

Corner, gate and end posts

• Corners take the tension of two fence directions — brace them with diagonal rails or a 6×6.
• Gate posts carry the full gate weight on a hinge — use 3+ bags of concrete and a 6×6 for heavy gates.
• End posts are where the fence starts and stops — treat them like corners.
• Line posts just hold pickets and rails; interior posts can use packed gravel in good soil, but concrete everywhere is simpler.

Mistakes that sink fences

• Shallow holes — the 1/3 rule is a minimum, and the frost line overrules it in winter.
• Skipping corner braces — a corner post without bracing leans by next season.
• Concrete above grade — water pools at the post base and rots the wood; slope the concrete away from the post.
• Not checking utility lines — call 811 before you dig; one auger hit costs far more than the call.
• Buying bags by guess — one hole at 4 bags and the next at 1 leaves a wavy fence line.

Set it once, set it straight

Run your fence length through the fence post spacing calculator — post count, hole depth and concrete bags in one pass. Then brace the first post plumb in both directions and the rest of the line follows it.