Fence Calculator
Enter your fence length and post spacing to get posts, sections, rails, pickets, and concrete bags. Everything updates as you type.
Concrete assumes 2 bags per post, the common rule for a 4×4 post in an 8-10 in hole. Picket and rail counts run the full fence length; if a gate opening replaces a section, subtract pickets and rails for that span by hand.
How to calculate fence posts and pickets
Start with the number of post-to-post spans. Divide total fence length by post spacing and round up, since a fence almost never divides evenly. Add one more post to close the last span, then add two posts for each gate opening:
Pickets depend on width, not spacing. Convert the fence length to inches, then divide by each picket's width plus the gap you're leaving between pickets:
Rails run horizontally between posts, so each section gets the same number of rails regardless of how wide it is. Multiply the section count by rails per section (2 for a low picket fence, 3 for a 6 ft or taller privacy fence) to get the total.
Pickets per 8 ft section
An 8 ft section is 96 inches of rail. Divide that by picket width plus gap to see how many pickets fill one section.
| Picket width | No gap | 1/4″ gap | 1/2″ gap |
|---|---|---|---|
| 3.5″ | 28 | 26 | 24 |
| 5.5″ | 18 | 17 | 16 |
| 7.25″ | 14 | 13 | 13 |
Post hole depth and diameter
Hole depth is roughly a third of the post's height above ground, with a 2 ft floor for a 6 ft fence. Diameter runs about three times the post's width so there's room for concrete on every side.
| Fence height | Hole depth | Post length needed | Hole diameter (4×4 post) |
|---|---|---|---|
| 4 ft | 2 ft | 6 ft | 10.5″ |
| 6 ft | 2 ft | 8 ft | 10.5″ |
| 8 ft | 2 ft 8″ | 10 ft 8″ | 10.5″ |
A 6×6 post is 5.5″ actual width, so its hole should run about 16.5″ across. Before digging any hole, call 811 and wait for your utility lines to be marked. It's free, and it's the only way to know what's buried along your post line.
Frequently asked questions
Should I space fence posts 6 ft or 8 ft apart?
8 ft spacing uses fewer posts and costs less, and it's standard for most residential wood privacy fences on level ground. Drop to 6 ft spacing on sloped or windy sites, with taller fences (7 ft and up), or with a heavier rail package: the shorter span keeps rails from sagging and gives the fence more resistance to wind load.
How deep should I set fence posts?
Set the hole about a third as deep as the post's exposed height above ground, with a 2 ft minimum for a 6 ft fence. A 6 ft fence needs a 2 ft hole, so the post itself should be about 8 ft long. Check your local frost line too; in cold climates the hole may need to go below it regardless of fence height.
How many bags of concrete does one fence post need?
Plan on 2 bags of 50 lb fast-setting concrete mix per post, for a standard 4x4 post in an 8-10 in diameter hole. Larger posts, wider holes, or deeper holes need more concrete; check the mix's yield-per-bag figure on the label and compare it against your hole's volume.
Does a board-on-board fence need more pickets?
Yes. Board-on-board style overlaps each picket with its neighbor, usually by about a third of the picket's width, so it takes roughly 30% more pickets than a butt-jointed privacy fence of the same length. Add that percentage to this calculator's picket count before ordering.
Do I need to call 811 before digging fence post holes?
Yes, in the United States call 811 at least a few business days before digging, and wait for the utility locate to be marked. It's free, and it's the only way to know whether a gas, electric, water, or communications line runs through your post line before an auger finds it.
Buying the rails and posts by the piece? The linear foot calculator totals up running feet across mixed lengths. Cutting your own pickets or rails from rough lumber instead of buying dimensional stock? The board foot calculator prices out the wood.