Fence Calculator

How fence materials are calculated

Sections = fence length ÷ post spacing, rounded up · Posts = sections + 1 (+ 1 per gate)
Rails = sections × rails per section
Pickets = fence length (in) ÷ (picket width + gap), rounded up
Concrete per hole = hole volume − post volume

A straight run of fence has one more post than it has sections. Every corner and gate also needs a post, and corner and gate posts are often set deeper or larger because they carry more load. Measure the fence line with a long tape or a measuring wheel and mark the corners before you count.

Worked example: 100 ft privacy fence

• Sections: 100 ÷ 8 = 12.5, so 13 sections and 14 posts.
• Rails: 13 × 3 = 39 rails (8-ft 2×4s).
• Pickets: 100 ft = 1,200 in; 1,200 ÷ 5.5 = 218.2, so 219 pickets of 1×6. Add 5–10% for split or warped boards.
• Concrete: a 10 in hole 24 in deep holds π × 5² × 24 = 1,885 cu in; a 4×4 post (3.5 × 3.5 in) takes up 294 cu in, leaving 1,591 cu in = 0.92 cu ft per post. For 14 posts, 12.9 cu ft, or 22 bags of 80 lb (0.6 cu ft each).

If you mix one post at a time, round up per hole instead: two 80 lb bags per hole means 28 bags. Buying a couple of extra bags is cheap insurance.

Post depth and spacing

A common rule of thumb is to bury about one third of the post's length, and at least 24 in, with the hole about three times the post's width. In cold climates, set the bottom of the hole below the local frost line so frost heave does not lift the posts. Post spacing of 8 ft suits standard 8-ft rails; 6 ft is stiffer and is often used for tall privacy fences and in windy areas. Your local building department or HOA may also limit fence height and require a permit; call your local utility-locating service (811 in the US) before you dig.

Picket spacing for a picket fence

For an open picket fence, choose the gap and the calculator counts the pickets. A 3½ in picket with a 2½ in gap repeats every 6 in, so 100 ft needs 200 pickets. Many pool-barrier codes limit gaps to under 4 in; check the rules where you live.

Shopping list

• Posts: pressure-treated rated for ground contact, or galvanized steel posts.
• Rails and pickets, plus 5–10% extra pickets.
• Concrete or gravel for the holes, and a few inches of gravel under each post for drainage.
• Exterior-rated screws or galvanized nails, gate hardware and post caps.

Step by step: planning a fence

1. Check property lines, permits and HOA rules, and call 811 (US) before digging.
2. Measure the fence line and mark corners, ends and gates.
3. Choose post spacing and the number of rails for the fence height.
4. Count posts, rails and pickets, adding extra pickets for damage.
5. Work out the concrete or gravel for the post holes.

Fence styles and materials

• Privacy fence: pickets butted tightly together, usually 6 ft high, with three rails. Board-on-board styles overlap the pickets and need about 1.5 times as many.
• Picket fence: spaced pickets about 3–4 ft high, with two rails.
• Horizontal fence: boards run between posts instead of rails; count boards by the fence height divided by the board width plus the gap.
• Vinyl and metal panels: sold as complete sections with matching posts, so you only need the number of sections, posts and gates.

Common mistakes

• Counting posts equal to sections. A straight run always needs one more post.
• Forgetting corner and gate posts in fences that turn or have openings.
• Using the nominal picket width: a 1×6 is 5½ in wide, not 6 in, which changes the count by about 9%.

Frequently asked questions

Sources

• Premixed concrete bag yields printed by major US manufacturers (80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft, 50 lb ≈ 0.375 cu ft).
• American Softwood Lumber Standard, NIST PS 20: dressed sizes (4×4 = 3½ × 3½ in; 1×6 = ¾ × 5½ in).
• Common Ground Alliance, 811 'Call Before You Dig' (US).

Last reviewed 20 October 2026. Results are estimates; see our disclaimer.