Posts and sections
Fence calculator
Add a run for each straight length of fence. The calculator counts posts, sections, rails and pickets, shares corner posts between runs, and works out the concrete going in the ground.
OrderExact · https://orderexact.com/fencing/
Posts are counted, not divided
A 100 foot run at 8 foot spacing is 12.5 spans, which rounds up to 13 sections — and 13 sections need 14 posts, because a fence has a post at both ends. Dividing the length by the spacing and stopping there leaves you one or two posts short on every run.
Where two runs meet at a corner they share a post. Tell the calculator which ends of each run join another and it counts that post once. A fence that closes into a rectangle ends up with exactly as many posts as sections, which surprises people the first time they see it.
Spacing is a target, not a rule
That 100 foot run does not have to be twelve 8 foot spans and one 4 foot stub. Thirteen even spans of 7 feet 8 inches uses exactly the same posts and looks deliberate instead of accidental. Set the corners and ends first, measure what is left, and divide it evenly.
Shorten the spacing rather than lengthening it where the fence is solid privacy board, where it runs across a slope, or where it is exposed to wind. A solid fence is a sail, and the load ends up in the post holes.
The concrete is the part nobody budgets for
A 10 inch hole 30 inches deep holds about 1.36 cubic feet. The post takes some of that back — a 4x4 in that hole displaces 0.21 cubic feet, so the concrete needed is about 1.15 per hole. Ignore the post and you over-order by roughly a fifth on every hole, which across 14 posts is most of a wheelbarrow.
Depth is a code question wherever the ground freezes: a footing above the frost line will lift, and a fence that lifts unevenly never comes back straight. Check the frost depth for your area before you dig.
Once you have the cubic feet, the concrete calculator turns it into bag counts and tells you when it is worth ordering ready-mix instead.
Before you dig
Have the utilities located. It is free in most places, it is legally required in many, and a post hole is exactly deep enough to find a gas or fiber line.
Confirm the property line before you set a post rather than after. Moving a fence that is six inches over a boundary means digging out every concrete footing you just poured, and boundary disputes over fences outlast the fences.
Common questions
How many fence posts do I need?
One more than the number of sections on each run. A 100 foot run at 8 foot spacing is 13 sections and 14 posts. Where runs meet at a corner they share a post, which this calculator accounts for.
How far apart should fence posts be?
Six to eight feet for a wood fence, with eight as the usual maximum. Go closer for solid privacy fences, slopes and exposed sites, because a solid fence catches wind like a sail.
How deep should a fence post go?
A common rule is a third of the post length in the ground, and always below the frost line where the ground freezes. Frost depth is local, so check with your building department.
How much concrete does a fence post need?
About 1.15 cubic feet for a 4x4 in a 10 inch hole 30 inches deep, once you subtract the space the post itself takes up. The calculator works this out per hole and for the whole fence.
How many pickets do I need?
Divide the total fence length by the picket width plus the gap. At 5.5 inch pickets with a half inch gap that is exactly two per foot, so a 100 foot fence takes 200.
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