Fence Calculator

How to use it

1. Measure each run. A run is a straight stretch between corners or between a corner and the house. Measure along the line the fence will take, and add a row per run; corner posts are counted where runs meet.
2. Set the post spacing. Eight feet on centre for most wood fences and panel fences; six feet for tall fences in wind, heavy panels or soft ground.
3. Choose rails and pickets. Two rails for fences up to 5 ft, three for taller. Enter the picket's actual face width (5 1/2 in for a nominal 1 x 6, 3 1/2 in for a 1 x 4) and the gap between pickets, 0 for a privacy fence. For a panel fence, set the picket width to 0.
4. Add gates. Width and how many. Each gate adds one post (it hangs between two, and one is already a line post) and its opening comes out of the picket run.
5. Set the hole size. Diameter, depth of the concrete, and the post size, so the post's own volume is subtracted. Pick the bag size you will buy.
6. Read the list. Posts, rails, pickets before and after waste, gate posts and concrete bags, with a per-run breakdown and a materials total when you enter prices.

Post spacing

Posts are spaced to suit the rails. Dimensional lumber comes in 8 ft lengths (and 16 ft, which cuts to two), and prebuilt panels are 8 ft wide, so 8 ft on centre wastes nothing. The calculator divides each run by the spacing and rounds up to whole sections, which is what you do on the ground: a 50 ft run at 8 ft is seven sections, and you either shorten the last one or spread the difference across all of them. Each run gets one more post than it has sections; where two runs meet at a corner, the corner post serves both, and you can drop one post from the total for each corner, or let the spare be the one you keep. Six-foot spacing is worth the extra posts for a 6 ft solid fence in an exposed spot, since a privacy fence is a sail, and for heavier materials such as composite boards.

Picket math

Pickets per foot is the picket width plus the gap, divided into 12. The nominal sizes mislead: a 1 x 6 picket is 5 1/2 in wide and a 1 x 4 is 3 1/2 in. Butted 5 1/2 in pickets for a privacy fence run 2.18 per foot; a traditional picket fence of 3 1/2 in boards with 2 1/2 in gaps runs 2.00 per foot. The calculator counts pickets across the whole run rather than per section, so the fractional picket at the end of each section is not rounded up eight times over. Board-on-board and shadowbox fences overlap pickets on both sides of the rails and need roughly 1 1/2 to 2 times as many; estimate them by entering the effective spacing, or run the calculator twice. Pickets also shrink as they dry: a wet-treated 5 1/2 in board can lose a quarter inch, so a fence butted tight in spring has gaps by autumn. Leave the gap or accept it.

Gates

A gate is a hole in the fence between two posts. The hinge post carries the gate's full weight as a lever, so it is the one post on the fence worth upsizing to a 6 x 6, setting deeper and bracing with more concrete; the latch post takes the slam. Common widths are 3 ft for a walk gate, 4 ft to get a mower through, and 10 to 12 ft as a double gate for a vehicle. Set the gate so one of its posts falls where a line post would go anyway, and only the other is extra: the calculator adds one post per gate and takes the gate width out of the picket count. The gate itself, whether a kit or built on site from the same pickets, is bought or counted separately, along with hinges, a latch and, for double gates, a drop rod.

Concrete per post

Each hole is a cylinder with a post in it, and the concrete is the difference. The usual hole is about three times the post width, so 10 to 12 in for a 4 x 4, and the depth is a third of the fence height plus whatever the frost line demands. Many installers put 4 to 6 in of gravel in the bottom for drainage and set the post on it, so the concrete column is shorter than the hole; enter the concrete depth. For a 12 in hole with 30 in of concrete around a 4 x 4, the calculator finds 1.75 cubic feet per hole, which is 4 of the 60 lb bags or 3 of the 80 lb bags. Multiply by every post, gate posts included, and the bags add up fast, which is why fence crews buy concrete by the pallet. Fast-setting mix can be poured dry into the hole and watered in; its 50 and 60 lb bags are listed at the same yields as ordinary concrete mix.

Bag yields come from:

• QUIKRETE Concrete Mix (No. 1101) data sheet (read 2026-10-05)
• Sakrete High-Strength Concrete Mix technical data sheet (read 2026-10-05)

Worked example: a privacy fence on three sides

A 6 ft privacy fence along the back (60 ft) and both sides (40 and 60 ft) of a yard, posts 8 ft on centre, three rails, butted 5 1/2 in pickets, one 4 ft gate, 12 in holes with 30 in of concrete around 4 x 4 posts, and 5 percent extra on the pickets:

The three runs total 160 ft and 21 sections, which takes 24 posts counted run by run, plus 1 more for the gate: 25 in all. Three rails per section is 63 rails. The pickets cover the fence less the gate opening: 341 before waste, 359 to buy. The 25 holes need 43.8 cubic feet of concrete, or 73 of the 80 lb bags. Two corners where runs meet could each share a post, so you may buy two fewer posts than the per-run count; the calculator lists the conservative number and flags it in the result.

Mistakes people make

• Using nominal picket widths. A 1 x 6 is 5 1/2 in. Using 6 in under-counts pickets by about 8 percent.
• Posts too short. Height above ground plus depth in the ground plus a little to trim. A 6 ft fence usually wants 8 ft posts at least.
• Stretching the spacing. Nine or ten feet between posts saves posts and sags rails.
• Treating gate posts like line posts. Upsize, deepen and concrete them.
• Forgetting the frost line. Posts set above it heave. Ask the local building department.
• Buying exactly the picket count. Some boards in every bundle are unusable. Five percent.