Fence Calculator

How to calculate fence posts, rails and pickets

A straight fence run is a row of equal sections. Divide the length by the post spacing and round up to get the number of sections. A run of n sections needs n + 1 posts, because the last section also has a post at its far end. That is the classic mistake: 100 feet with posts 8 feet apart is 100 ÷ 8 = 12.5, which rounds up to 13 sections, and 13 sections need 14 posts, not 13. With 3 rails per section the same run needs 13 × 3 = 39 rails.

Because sections are rounded up, the real spacing comes out a little under the number you typed. The 13 sections of the 100 foot run are 7.69 feet apart, not 8. The calculator shows that actual spacing in the result.

Example: 100 feet of picket fence with one gate

One straight run of 100 feet has a 4 foot gate. The posts are 8 feet apart, the fence has 3 rails per section and 5.5 inch pickets with 0.5 inch gaps. It stands 6 feet above ground, the holes are 10 inches wide, and you add 10% waste. These are the figures you get if you type the same values into the calculator.

How far apart should fence posts be?

Millard Lumber, a lumber retailer, says to set fence posts about 6 to 8 feet apart, and that the right figure depends on the type of fence, the terrain and the purpose. Family Handyman, an informational site, gives 8 feet as the standard spacing for wood fences and warns that rails sag when posts are too far apart. Both were checked in October 2026. Tighter spacing means more posts, as this 100 foot run shows.

Posts and rails by fence length

This table assumes one straight run, no gates, posts 8 feet apart and 3 rails per section.

Gates, corners and fence ends

• Gates. Enter the whole line, gate openings included, and the number of gates in each run. The calculator subtracts the gates, counts the sections of the rest and gives every gate two gate posts. A gate splits its run in two, so it adds one post to the count. It also assumes there is fence on both sides of each gate.
• Corners. Enter every straight stretch as its own run. Where two runs meet they share one post, so the calculator takes one post off per corner. A fence that closes into a loop needs at least 3 runs and has as many corners as runs.
• Short pieces. The sections come from the total net length of each run. If a gate sits close to one end, that short piece may need its own section. Count it as a separate run.
• Ends. The two far ends of an open run each get a post. A run that is not joined to another at either end has 2 end posts.
• Panels. The Outdoor Essentials panel worksheet counts 1 post per panel, plus 1 to end the run and 1 for each gate, and subtracts the gates from the length. Its example turns 120 feet of panels 8 feet wide into 15 panels and 17 posts. The calculator gives the same 15 panels and 17 posts for a 124 foot run with one 4 foot gate. The worksheet says panels are typically 6 or 8 feet wide.

For horse fences, Penn State Extension says a typical line post is set 36 inches deep, while corner and gate posts, which handle greater loads, are about 25 percent larger in diameter and set deeper, often to 48 inches. That guide is about horse fences, so it is not a rule for a backyard. The hole depth box lets you type your own figure.

How many pickets or boards do you need?

Every picket takes its own width plus one gap, except the last one, which has no gap after it. So n pickets cover n × width + (n − 1) × gap. The calculator finds the smallest n that covers the net length of each run. A common shortcut divides the length by (width + gap). For 96 feet with 5.5 inch pickets and 0.5 inch gaps that gives exactly 192, but 192 pickets cover only 1,151.5 inches of the 1,152 needed, so 193 is the right count. The widths below are examples for the arithmetic, so measure your own pickets.

How deep should fence posts be, and how much concrete?

Millard Lumber says to set wood posts with about one third of their total length buried, and that this matters most for corner posts and posts that carry heavy loads or wind. If one third is underground, two thirds stand above it, so the hole depth is half the height above ground and the post is 1.5 times that height. The same guide also says to keep the bottom rail at least 2 inches off the ground.

The calculator treats each hole as a cylinder. It does not subtract the volume of the post, so the figure is a ceiling. To turn cubic feet into bags, open the concrete calculator, choose the “Round column” tab, type the hole diameter and depth, and set “Number of identical pieces” to the number of posts. That calculator offers 40, 60 and 80 lb bags. For a 50 lb bag, QUIKRETE gives a yield of 0.375 cubic feet, so divide the cubic feet by 0.375.

Check local rules before you build

This calculator counts materials. It does not know the fence height your city allows, how far from the property line you must build, or what your homeowners association requires. Those rules change by city, county and HOA, so ask the building department and your HOA before you buy. The Millard Lumber guide gives the same advice and also says to know exactly where your property line is before you start. The calculator shows no prices, which change by store and region.

Frequently asked questions