About the Fence Calculator
This fence calculator turns the length of a fence line into a complete wood-fence materials list: the number of posts and sections, horizontal rails, pickets, and bags of concrete to set the posts. Enter the total run, post spacing, rails per section and picket size, and it adds up the materials and cost so you can compare a DIY build with a contractor quote.
It works for privacy fences (pickets butted together), spaced picket fences and shadow-box styles, and it is useful for homeowners, landlords and handymen planning a new fence or replacing a run of old boards. Post holes are assumed to be round, with a 4×4 post set in concrete; the concrete volume subtracts the space the post itself takes up.
For a fence with corners, run the calculator once per straight side, or accept that each corner shares a post and remove one post per corner from the total. Gates need their own heavier posts and hardware, and local rules may govern fence height and setbacks from property lines.
With the default inputs, the fence posts is 20. Change any value above to recalculate instantly.
How to use the fence calculator
- 1Measure the total length of the fence line in feet.
- 2Choose post spacing and the number of rails per section.
- 3Enter picket width and gap (0 for a privacy fence).
- 4Enter the post hole size and the concrete bag you will use.
- 5Add prices to see the total material cost and cost per foot.
Formula and method
A straight fence of length L with posts every s feet has ⌈L ÷ s⌉ sections and one more post than sections. Rails are sections × rails per section. Pickets cover the full run: each picket takes its own width plus the gap, so the count is the length in inches divided by (picket width + gap), plus a waste allowance for splits and cuts.
Each post hole is treated as a cylinder of radius r and depth d, minus the volume of the 3½ × 3½ inch post, converted from cubic inches to cubic feet by dividing by 1,728. The total concrete is divided by the bag yield (about 0.375, 0.45 and 0.6 cu ft for 50, 60 and 80 lb pre-mixed bags) and rounded up.
- L
- Fence length (ft)
- s
- Post spacing (ft)
- p, g
- Picket width and gap (in)
- r, d
- Post hole radius and depth (in)
Worked examples
150 ft privacy fence, posts every 8 ft
150 ÷ 8 = 18.75, so 19 sections and 20 posts with 38 rails. Butted 5½ in pickets need 327.3, or 344 with 5% waste. Each 10 in × 24 in hole takes 0.92 cu ft of concrete, so 20 posts need 31 bags of 80 lb mix, and materials total $1,822.
100 ft spaced picket fence with 3 rails
A 100 ft run at 8 ft spacing has 13 sections and 14 posts, needing 39 rails. Each picket plus gap spans 6 in, so 200 pickets plus 5% is 210. The posts take 12.9 cu ft of concrete, or 35 bags of 50 lb mix; materials cost $997.
200 ft fence, posts every 6 ft in smaller holes
At 6 ft spacing, 200 ft needs 34 sections and 35 posts. Holes 8 in wide and 18 in deep hold about 0.4 cu ft of concrete each (13.9 cu ft total, 24 bags). With 459 pickets and 68 rails the materials cost about $2,332.
Frequently asked questions
How many fence posts do I need?+
Divide the fence length by the post spacing, round up, and add one. For example, 100 ft at 8 ft spacing needs 13 sections and 14 posts. Add an extra post for each gate and each corner if you calculate sides separately.
How far apart should fence posts be?+
Wood fence posts are usually 6 to 8 feet apart on center. Eight feet matches standard rail and panel lengths; closer spacing makes a stiffer fence in windy or soft-soil areas.
How many bags of concrete per fence post?+
A 4×4 post in a 10-inch hole 2 ft deep needs about 0.92 cu ft of concrete — roughly 1½ bags of 80 lb mix or 2½ bags of 50 lb mix. Deeper or wider holes need proportionally more.
How many pickets are in a foot of fence?+
With 5½ inch pickets butted together, you need about 2.2 pickets per linear foot. Spaced pickets need fewer: a 3½ inch picket with a 2½ inch gap uses 2 per foot.
How deep should fence posts be?+
A common rule is to bury about one-third of the post’s above-ground height — 2 ft for a 6 ft fence — and to go below the frost line in cold climates. Check local code and utility locations before digging.