ClutchCalcs

Construction

Fence Calculator

Building a wood privacy fence is a one-weekend project if you walk into the lumberyard with the right material list, and a four-weekend disaster if you don't. Plug in your total fence run, pick a post spacing and picket width, and this calculator gives you a complete shopping list: posts, pickets, rails, and bags of concrete to set the posts.

How the math works

A wood privacy fence breaks into four components — posts, pickets, rails, and concrete — and each has a different unit of measure.

  • Posts = ceiling(length ÷ spacing) + 1. The +1 accounts for the end post. A 100-ft fence at 8-ft spacing needs 13 + 1 = 14 posts.
  • Pickets = (length in inches) ÷ (picket width + gap). For 1×6 pickets butted together with no gap on a 100-ft fence: 1200 inches ÷ 5.5" = 219 pickets.
  • Rails = length × number of rails. A 100-ft fence with 3 rails per section = 300 linear feet of 2×4 rail material.
  • Concrete = 2 bags of 50-lb fast-setting concrete per post. A 14-post fence needs 28 bags.

Post spacing — 6 ft vs 8 ft

8-ft spacing is the standard for residential wood privacy fences because lumber comes in 8-ft sections. It's cheaper (fewer posts, fewer holes), but it puts more wind load on each post and the rails can sag if you use thin lumber. Use 8-ft spacing on shorter fences (4-5 ft), or 6-ft fences in low-wind locations.

6-ft spacing costs about 30% more in posts and concrete, but the fence is dramatically stiffer and the rails (now 6-ft pieces) don't sag. Use 6-ft spacing on tall fences (6-8 ft) in windy areas, or anywhere you want a "built-once" fence that lasts decades.

Picket width matters less than people think — 1×6 pickets (5.5" actual) cover area faster (fewer pickets to nail) but show more wood grain. 1×4 pickets (3.5" actual) cost more per linear foot of fence but produce a more refined look. Stick with 1×6 unless you're chasing a specific architectural style.

How to use this calculator

  1. Measure the actual run. Walk the line with a measuring wheel or tape — don't estimate from the property survey alone. Property lines and where you actually want the fence often differ by a foot or two.
  2. Subtract gates. If you're putting in a 4-ft gate, deduct 4 ft from total fence length and order a pre-built gate kit separately. Don't try to make a gate from regular fence sections — it'll sag.
  3. Account for corners. Each corner needs a post but doesn't add fence length. The calculator already includes the "+1" for end posts, but for L-shaped or U-shaped runs, count each leg separately and combine.
  4. Add 10% to picket count. Pickets get cracked from the lumberyard, you'll mess up cuts, and you want spares for future repairs.
  5. Pad rails by ~5%. You'll lose some to cut waste and bad lumber.

Common scenarios

100-ft 6-ft tall privacy fence, 8-ft spacing, 1×6 pickets. 14 posts (4×4 × 8'), 219 pickets, 300 ft of 2×4 rails (75 boards × 4-ft pieces or 50 boards × 8-ft pieces), 28 bags of concrete. At 2025 prices roughly $1,400-$2,000 in materials depending on lumber grade.

200-ft back yard fence with two gates (3-ft + 4-ft). Effective fence length = 193 ft. Posts: 26 + 4 gate posts (corners and gate frames need 6×6 instead of 4×4) = 30 total. Pickets: 421. Rails: 579 ft. Concrete: ~60 bags. Material cost lands $3,000-$4,500.

50-ft side fence between houses, 6-ft tall, 6-ft spacing for stiffness. 10 posts, 110 pickets, 150 ft of rails, 20 bags of concrete. The tighter spacing matters here because the fence is exposed to wind funneling between buildings.

FAQ

How deep should fence posts be? +
One-third of total post length below grade, and always below the local frost line. A 6-ft fence uses 8-ft posts buried 24-30 inches deep. In cold climates (Minnesota, Maine, Montana) the frost line can be 48 inches deep — use 9 or 10-ft posts there. The "1/3 buried" rule is the structural minimum; longer is better for wind resistance.
How much concrete per post? +
Two 50-lb bags of fast-setting concrete fills a typical 10" diameter × 30" deep post hole around a 4×4. For 6×6 posts or deeper holes (frost line jobs), plan three bags. The fast-set kind sets in 20-40 minutes and doesn't need to be pre-mixed — pour it dry around the post, then add water on top per the bag instructions.
Pressure treated, cedar, or redwood? +
Pressure treated pine is the workhorse — cheapest, lasts 15-25 years in ground contact, and accepts paint or stain. Cedar costs 50-100% more, has natural rot resistance, and weathers to a silvery gray if left untreated. Redwood is the premium option, gorgeous, and now hard to source east of the Rockies. For posts, always use ground-contact-rated pressure treated regardless of what species you use for pickets.
Nail, screw, or bracket the rails? +
Screws — galvanized or stainless steel deck screws — last 3-5x longer than nails before pulling out. Toe-screwing into the post is fine for standard fence sections. For premium builds, use stainless steel rail brackets (~$3 each) that hold the rail to the post mechanically. Skip nails entirely; they back out within a few seasons.
Do I need a permit? +
Most municipalities require permits for fences over 6 feet, and many HOAs have rules about height, materials, and "good side out" orientation. Check before you dig. Also call 811 ("Call Before You Dig") 2-3 business days before you start — underground utility marking is free and prevents extremely expensive accidents.
Can I install a fence on a slope? +
Yes, two ways. Stepped: keep each section level, dropping in stair-steps along the slope. Looks clean but leaves triangular gaps under the bottom rail. Racked: the rails follow the slope at an angle, and the pickets stay vertical. Racked sections need pickets cut individually at the bottom — more work but no gaps. Steep slopes (over 1:3) almost always need racked construction.
What about gates? +
A standard 4-foot gate uses 6×6 posts (or doubled 4×4s) for the gate jambs because the weight cantilevers off one side. Pre-built welded steel gate frames last longest. Always install the strike side with the post slightly leaning toward the gate so it self-closes against gravity by 1/8" or so — over time it'll settle plumb.
How long does a wood fence last? +
10-15 years for an untreated pine fence with no maintenance. 20-30 years for a cedar or pressure-treated fence that gets re-stained every 3-5 years. Posts are usually the failure point — they rot at ground level long before the pickets or rails fail. Setting posts in concrete extends life dramatically over gravel-only post bases.