Fence calculator
Posts, rails, pickets and the concrete to set them — for any straight run of fence.
Calculator
Detailed breakdown
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How to use this calculator
Measure
Enter the total run in feet and your post spacing. Eight feet is standard for wood fence.
Calculate
Once you hit calculate, results update as you type. Change any number to compare options instantly.
Order
Print the estimate and take it to your supplier. Quantities are rounded up so you don't come up short.
Buy your posts two feet longer than the fence
A 100 foot fence at 8 foot spacing needs 13 sections, twelve full bays and a short one, so 14 posts: one more than the number of gaps. Three rails per section is 39 rails, and with 5.5 inch boards butted tight you need 219 pickets for privacy. Setting those 14 posts takes about 39 bags of 60 lb concrete.
Buy your posts two feet longer than the finished height. A 6 foot fence needs 8 foot posts, because a third of the post — or 2 feet, whichever is deeper — goes in the ground. On an 8 foot post that third is 2 feet 8 inches, not 2 feet, and the concrete figure above follows that rule rather than a flat 2 feet. This is the single most common ordering mistake on a fence, and you find out about it on installation day.
Depth isn't really about the fence — it's about frost. If your footing sits above the frost line, the ground lifts it every winter and drops it every spring, and within a few seasons the line is visibly wavy. Look up the frost depth for your county and dig below it, even when that means going well past 2 feet.
What goes in the ground has to be rated for it. Pressure-treated lumber comes in two retentions, and only the ground contact grade belongs in a post hole. Above-ground grade rots at the soil line in a few years, which is exactly where a fence post fails and exactly where you cannot repair it without pulling the whole section. Check the tag on the end of the post rather than assuming, since both grades sit in the same rack and look identical.
Gates aren't in this count, and they carry a swinging load that line posts never see: gate posts want a wider, deeper hole and often a larger post. Sloped ground isn't in it either. You either rack the fence, following the grade with parallelogram sections, or step it, which needs taller posts and leaves triangular gaps at the bottom. Both change the picket count, so measure the slope before you order.
Frequently asked questions
How many posts for a 100 foot fence?
Fourteen at 8 foot spacing. A hundred feet does not divide evenly by eight, so you get 12 full bays and a 4 foot one — 13 sections — and you always need one more post than sections.
How deep should fence posts be?
A third of the post length or 2 feet, whichever is deeper, and always below your local frost line. Shallow footings heave and the fence goes wavy.
How long should fence posts be for a 6 foot fence?
Eight feet. Buy posts two feet longer than the finished height so a third of the post can be buried.
How much concrete per fence post?
About 1.2 cubic feet for a 10 inch hole 2 feet 8 inches deep, which is roughly three 60 lb bags per post once the post's own volume is taken out. A 10 to 12 inch hole is right for a 4x4; 8 inches leaves too little concrete around the post.
How many pickets for 100 feet of privacy fence?
About 219 using standard 5.5 inch boards butted with no gap. A spaced picket fence with a 2 inch gap needs far fewer.
What lumber should fence posts be?
Pressure-treated to a ground contact retention. The above-ground grade looks the same and sits in the same rack, but it rots at the soil line, which is the one place you cannot repair without pulling the section.
Are gate posts different from line posts?
Yes. A gate post carries a swinging load that line posts never see, so it wants a wider and deeper hole, and often a heavier post. This calculator sizes line posts only.
Sources
Formulas and material assumptions on this page follow published industry guidance: