Fence Calculator: Posts, Pickets & Rails
A fence needs three different materials — posts, pickets and rails — each with its own count and its own price, and getting any one of them wrong stops the whole job. This free fence calculator works out all three at once: enter your fence length, choose your post spacing and picket gap, and it tells you exactly how many posts, pickets and rails to buy, plus the concrete for the holes and the total estimated cost.
Fence Material Calculator
How to Use This Fence Calculator
Measure the full run of your fence in feet, going around corners the way the fence will run. Choose your post spacing — 8 feet is the economical standard, 6 feet if the fence is tall or the site is windy. Enter your picket width (5.5 inches is standard) and the gap you want between pickets (half an inch gives a classic privacy fence with a little daylight).
Pick 2 rails for a 4-foot fence or 3 rails for a 6-foot fence. If you know prices for the posts, pickets and rails, enter them for a full cost estimate — otherwise leave them blank. Click Calculate and the tool shows every count, plus an estimate of the concrete for the post holes.
The Fence Calculation Formula
Posts: divide the length by the spacing and round up, then add one for the far end — posts = ceiling(length ÷ spacing) + 1. Pickets: each picket plus its gap occupies (width + gap) inches, so pickets = length × 12 ÷ (width + gap), rounded up. Rails run between posts, so rails = (posts − 1) × rails per section.
Worked example: a 100-foot fence with 8-foot post spacing gives 100 ÷ 8 = 12.5 — round up to 13 sections, plus one, so 14 posts. With 5.5-inch pickets and 0.5-inch gaps: 100 × 12 ÷ 6 = 200 pickets. With 3 rails per section: 13 × 3 = 39 rails. And 14 post holes at two 50 lb bags each means 28 bags of concrete.
Pro Tips for Building a Fence That Lasts
Set corner and gate posts first, in concrete, and let them cure a day before running your string lines. Corners take all the tension of the fence, so brace them and use extra concrete — a leaning corner post pulls the whole fence with it.
Before you dig: call 811 (in the US) to have underground utilities marked — it is free and required by law in most areas. Check your property line and local fence codes too: height limits, which side faces out, and permit requirements all vary by city, and an unpermitted fence can be an expensive mistake to remove.
Frequently Asked Questions
How many fence posts do I need for 100 feet?
With the standard 8-foot post spacing, a 100-foot fence needs 14 posts: 100 ÷ 8 = 12.5 sections, rounded up to 13 sections, plus one post at the end. Tighter 6-foot spacing would need about 18 posts.
How far apart should fence posts be?
Six to 8 feet is standard for wood privacy fences. Eight feet is the economical maximum — beyond that, rails sag between posts. Use 6-foot spacing in windy areas or for tall fences.
How many pickets do I need per 8-foot section?
With standard 5.5-inch pickets and a 0.5-inch gap (6 inches per picket), an 8-foot section needs exactly 16 pickets: 96 inches ÷ 6 = 16. That is 2 pickets per linear foot of fence.
How deep should fence posts be set?
Bury one-third of the post — a 6-foot fence needs holes 24 to 30 inches deep, and below your local frost line. Set posts in concrete (about two 50 lb bags per hole) or well-compacted gravel.