Fence Calculator

What the fence calculator counts

A wood fence is five piles of stuff, and the calculator works through them in the order you would build them: posts, rails, pickets, concrete and fasteners, then the cost of all five. Each count follows from the one before it.

• Posts divide the run into bays. A 150 foot run at 8 foot spacing is 18.75 bays, which rounds up to 19, and a fence always needs one more post than it has bays, so 20 line posts. Each gate adds 2 posts.
• Rails run post to post. A 6 foot fence carries 3 rails per bay, a 4 or 5 footer carries 2, and rail comes in 8 foot boards, so the linear feet get divided by 8 and rounded up.
• Pickets hang on the rails. The pitch, picket width plus gap, decides how many fit across the run.
• Concrete sets the posts: 2 bags of 80 lb mix per hole in normal soil.
• Fasteners are an allowance, roughly 2 screws per picket at every rail they cross.

The waste allowance defaults to 10 percent, which covers split boards, a mis-measured bay and the offcut the saw leaves. Sloped ground and diagonal layouts push that closer to 15 percent.

Worked example: 150 feet of 6-foot privacy fence

Take the default job: 150 feet of 6 foot dog-ear privacy fence, 5.5 inch pickets with a 0.25 inch gap, posts every 8 feet, one walk gate, and a 10 percent waste allowance.

That is $2,171 of materials, or $14.47 for every linear foot of fence. The pickets are more than half the bill, which is the line to watch when a supplier quotes you: a $0.50 difference per picket is $172 across this fence.

The same fence without the gate drops to 20 posts, 62 rail boards and 30 bags, about $1,988. Switching to 3.5 inch pickets at the same gap raises the picket count from 313 to 480 before waste, because the pitch drops from 5.75 inches to 3.75, and the material cost climbs to $2,628. The gap matters more than most people expect: closing it entirely saves 15 pickets, about $53, and gives up the drainage that keeps boards from cupping.

Run the calculator once with the prices from your own supplier and the estimate turns from a guide into a shopping list. Prices in the table are examples, not quotes, and lumber in particular moves with the season.

Posts: how many, how far apart, how deep

Post spacing is the decision that moves the post count the most, and 8 feet on center is the standard for a wood privacy fence. University of Georgia Extension guidance puts rail fences at 8 to 10 feet with wooden line posts set at least 2 feet deep. Spacing widens on flat, straight runs and tightens on slopes, curves and corners.

The counts above are line posts only, one more than the number of bays. Corner posts, a gate at each end and a break in the run all add posts, and every gate adds 2 of them because a gate hangs between its own pair.

Depth follows two rules and you dig to the deeper one. The first is the one third rule: a 6 foot fence wants 24 inches of post in the ground, since 12 x 6 / 3 = 24. The second is frost: where the ground freezes, the hole goes to the local frost line plus 6 inches, which is 36 inches or more across the northern states. The fence post depth calculator works the pair out for your fence height and frost line, and the post hole concrete calculator sizes the bags for any hole you end up digging.

Digging is where the day goes. Twenty two holes at 30 minutes each is 660 minutes, or 11 hours, and a two man auger cuts that to about 3 hours. And any hole 4 feet deep or more is a confined space: OSHA's trenching guidance requires a safe way in and out of excavations at that depth on job sites, and the same habit protects a homeowner. Never lean into a hole you cannot climb out of, and keep children and pets away from open holes overnight.

Pickets and rails: the two numbers that move most

Pickets are the biggest line on the bill and the easiest to miscount. The pitch is picket width plus gap, and the count is the run in inches divided by the pitch. For the example fence, 150 x 12 / 5.75 = 313 pickets, and 10 percent waste takes it to 344.3, so buy 345.

The table below leaves the gate out so the three layouts compare directly.

Three things to notice in that table. Narrow pickets nearly double the count, because the pitch drives everything. Closing the gap does not save pickets, it costs 15 more of them, about $53, and it gives up the drainage that keeps boards from cupping, which is why most installers keep at least a 0.25 inch gap on a privacy fence. And the per foot figures assume the same posts, rails and concrete, so the difference between rows is almost all pickets.

Rails are simpler. A 6 foot fence carries 3 rails and a 4 or 5 footer carries 2, with the top rail 2 to 3 inches below the post top. The example fence needs 3 x 150 = 450 feet of rail, plus 12 feet of frame for the gate, which is 462 feet. Rail comes in 8 foot boards, so 462 / 8 = 57.75, and with waste that is 63.5, so buy 64. Stagger the joints so two boards never end on the same post, or the fence develops a hinge at every eighth foot.

Concrete, screws and gates

Concrete is the part people under-order. A 9 inch hole, 36 inches deep with 6 inches of gravel in the bottom, around a 4x4 post, takes 0.892 cubic feet of mix. Twenty two holes take 22 x 0.892 = 19.6 cubic feet, and an 80 lb bag yields 0.6 cubic feet, so 19.6 / 0.6 = 32.7, which rounds up to 33 bags, about 2 per post. Wet, sandy soil or a 6x6 post pushes that up, and the bags are cheap insurance against a half-set post line.

Fasteners are the other small number that adds up. Two screws at every rail crossing on every picket is 345 x 6 = 2,070 screws, which is four or five 5 lb boxes of exterior deck screws. Ring shank nails work too and go in faster, but screws hold better when a board cups. Budget 5 minutes per picket to hang, level and fasten: 345 pickets at 5 minutes each is 1,725 minutes, just under 29 hours, and that is the single biggest labor item on the fence.

A 4 foot walk gate is a frame of 2x4s, three hinges, a latch and a diagonal brace, plus the 2 posts it hangs between. Hardware kits run $100 to $160 in most US stores, and the calculator carries $130. The brace matters: without a diagonal from the bottom hinge corner to the top latch corner, a wooden gate sags within two seasons. Add a drop rod or a cane bolt if the gate is on a slope, and set the gate posts an inch or two deeper than the line posts, because they carry a swinging load.

DIY or hire it out

The material estimate and the installed price live in different worlds. At $14.47 per foot, materials for the 150 foot fence come to $2,171. Installed wood privacy fencing in most US markets runs $25 to $45 per linear foot, so the same fence built by a crew lands between $3,750 and $6,750, and the difference is labor, equipment, disposal and the crew's speed.

The middle row is the one worth testing: an auger rental is $75 to $150 a day and removes the hardest third of the job. If the run is longer than 300 feet or the ground is rock or heavy clay, the hired number starts to look different, because that is exactly the ground that breaks DIY schedules.

If you take quotes, take them properly. The FTC's advice on home improvement scams is to get several written estimates that list materials and completion dates, check license and insurance, avoid choosing on price alone, and never pay the full amount up front. A deposit of a third is standard, with the balance due when the fence is done and you have walked it.

What the estimate leaves out

The calculator prices lumber, concrete and hardware. A real fence project has a second list, and it is worth writing down before the first hole:

• Permits and rules. Many cities require a permit above 6 feet or for any front yard fence, and an HOA can dictate height, color and style. One phone call to the building department settles both.
• Property line. A fence on the wrong side of the line can be ordered down. If the line is not obvious, a survey costs a few hundred dollars and is cheaper than moving 150 feet of fence.
• Utilities. Call 811 before digging. Locating buried gas, power and water lines is free, and it is the difference between a fence and a repair bill.
• Slope. A fence stepped down a hill uses more picket length and more rail than the flat measurement suggests. Add 5 to 10 percent for noticeably sloped runs.
• Removal. Tearing out an old fence adds a day and a disposal fee, and dump fees for a 150 foot run of old pickets are real money.
• Finish. Bare pressure treated pickets gray out in a year or two. Stain adds a second materials bill, which the fence stain calculator prices for the same run.

One last habit: buy the lumber in one trip and stack it flat for a day or two before building. Wet or bowed pickets are the reason the waste allowance exists, and a day of rest in the shade straightens most of them out. Then build the gate last, once the fence has settled, and the whole job holds its line for years.