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Fence Post Calculator
Use this free fence post calculator to plan a fence before you buy a single post. Enter the fence length, the post spacing, and any gates, and it works out how many posts, panels, and rails you need, plus how many bags of concrete to set them. It handles a straight run or a rectangular perimeter, wood or metal posts, and the common bag sizes, so your shopping list is right the first time.
| Item | Amount |
|---|---|
| Fence length (after gates) | 96 ft |
| Sections / panels | 12 |
| Posts | 14 |
| Rails (2 per section) | 24 |
| Concrete per post | 2 bags |
| Total concrete bags | 28 bags |
How it works
The calculator starts with the fenced length. For a straight run, that is the length you enter. For a rectangle, it is the perimeter, twice the length plus twice the width. Then it subtracts the gate widths, because a gate opening is not filled with fence panels. A 100-foot run with one 4-foot gate has 96 feet of actual fencing. This step matters: forgetting the gates is the most common reason a fence order comes up short on panels and long on posts.
Next it counts sections. The fenced length is divided by the post spacing and rounded up, because a partial section still needs a post at its end. With 96 feet of fencing and 8-foot spacing, that is exactly 12 sections. With 7-foot spacing, the same run would need 14 sections, since 96 divided by 7 is 13.7, rounded up. The spacing you choose is a trade-off: 8 feet is the standard for pre-built panels and uses fewer posts, while 6 feet is stronger and better for tall fences, windy sites, and heavy gates.
Posts come from the sections. A straight run needs one post at the start plus one at the end of every section, which is sections plus one. A closed rectangle needs one post per section, since the last section meets the first post again. Each gate adds one extra post, because a gate frame needs its own pair of posts, one for the hinges and one for the latch, on top of the run. So a 12-section straight run with one gate needs 12 + 1 + 1 = 14 posts.
Panels and rails follow from the sections. Each section takes one panel, or one set of pickets if you are building board by board, and two horizontal rails. Twelve sections therefore need 12 panels and 24 rails. If your fence design uses three rails per section, which some 6-foot privacy fences do, multiply the rail count by 1.5 and round up.
Concrete is worked out from the hole, not from a guess. The calculator assumes a 10-inch wide hole, 24 inches deep, which is a typical setting for a 4 by 4 wood post. The hole volume is about 1.09 cubic feet. The post itself takes up about 0.22 cubic feet, leaving about 0.87 cubic feet of concrete per post. Bag yields are about 0.375 cubic feet for a 50-pound bag, 0.45 for a 60-pound bag, and 0.6 for an 80-pound bag, so a wood post needs 3 bags of 50-pound mix, or 2 bags of 60-pound or 80-pound mix. Metal posts are slimmer, so they need slightly less concrete per hole, and the calculator adjusts for that. Always buy a few extra bags: a hole dug wider than planned eats concrete fast, and a half-set post cannot wait for a store run.
Depth deserves a word of its own. Bury at least one third of the post, with a minimum of 24 inches for a 6-foot fence, and go below the frost line in cold climates so freeze and thaw cycles do not heave the posts out of the ground. Check local rules before you dig, because some areas require 30 inches or more, and always call your local utility marking service before you put a post hole digger in the ground.
Posts = sections + 1 (+ 1 per gate) · Concrete per post = hole volume − post volume
Worked example
You are building a 100-foot straight wood fence with 8-foot post spacing, one 4-foot gate, and 80-pound bags of concrete.
Step 1: Fenced length — 100 − 4 = 96 feet of fencing.
Step 2: Sections — 96 ÷ 8 = 12 sections.
Step 3: Posts — 12 + 1 + 1 gate extra = 14 posts.
Step 4: Panels and rails — 12 panels and 12 × 2 = 24 rails.
Step 5: Concrete — a 10-inch by 24-inch hole holds about 0.87 cubic feet of concrete after the post. One 80-pound bag yields about 0.6 cubic feet, so 0.87 ÷ 0.6 = 1.45, rounded up to 2 bags per post. Total: 14 × 2 = 28 bags.
Buy 14 wood posts, 12 panels, 24 rails, and 28 bags of 80-pound concrete mix, plus a few spare bags for holes that come out wider than planned. If you switch to 6-foot spacing, the same run needs 16 sections, 18 posts, and 36 bags.
FAQ
How far apart should fence posts be?
Most wood fences use 6 or 8 feet between posts. Eight feet is the standard for pre-built panels and costs less because it uses fewer posts, while 6 feet is stronger and better for tall fences, windy sites, or heavy gates. Never space posts more than 8 feet apart for a wood privacy fence, or the rails will sag between posts.
How many bags of concrete do I need per fence post?
For a typical 10-inch wide hole 24 inches deep with a 4 by 4 wood post, you need about 0.87 cubic feet of concrete per post. That is 2 bags of 80-pound mix, 2 bags of 60-pound mix, or 3 bags of 50-pound mix per post. The calculator works this out from the hole volume and the yield printed on the bag.
How deep should fence posts be buried?
A good rule is to bury one third of the post, with a minimum of 24 inches for a 6-foot fence, and deeper where the ground freezes. In cold climates, set the post below the frost line so freeze and thaw cycles do not heave it out of the ground. Always check local codes, because some areas require 30 inches or more.
Do gates change the number of fence posts?
Yes. Each gate needs its own pair of posts, one for the hinges and one for the latch, and the gate opening takes the place of a fence section. The calculator subtracts the gate widths from the fence length before counting sections, then adds one extra post per gate for the gate frame.
Should I use wood or metal fence posts?
Wood posts are cheaper, easier to cut and attach rails to, and match a wood fence, but they can rot at ground level after 10 to 15 years. Metal posts last longer and resist rot and insects, but they cost more and need brackets to hold the rails. For a long-lasting fence, metal posts with wood panels are a popular compromise.