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lab.golamrabbani.org

Fence Calculator

Fence posts, rails, pickets, and concrete bag count from length and spacing.

Written by Golam Rabbani, Founder & Lead Engineer

Units:
Units

6 or 8 ft typical

Affects rail count

2 standard; 3 for ≥6 ft

5.5″ for 1×6 or 2×6

0 for shadow-box; 0.25–0.5 typical

4″ = 4×4

24–36″ typical

Roughly 3× post width

How to use this fence calculator

  1. Toggle imperial (ft) or metric (m) for the overall measurements.
  2. Enter total fence length and post spacing (6 or 8 ft is typical).
  3. Set fence height, rails per section, picket face width, and picket gap.
  4. Set the post-hole dimensions: post size, hole depth, and hole diameter.
  5. Press Calculate to see posts, rails, pickets, and concrete bag count.

About this fence calculator

The fence calculator estimates the four big-ticket materials for a wood fence: posts, rails, pickets, and concrete for setting posts. It divides the total length by post spacing (rounded up) to get the section count and adds one for the end post. Rails are sections × rails-per-section. Pickets are total length in inches divided by (picket width + picket gap). Concrete per post is the cylindrical hole volume minus the square post volume, summed across all posts, then divided by the 0.6 ft³ yield of an 80 lb bag.

Worked example: a 100-ft fence with 8-ft post spacing, 6 ft tall, two rails per section, 5.5″ pickets with 1/4″ gaps, 4×4 posts in 24″ deep × 10″ diameter holes. Sections = 100 ÷ 8 = 12.5 → 13. Posts = 14. Rails = 13 × 2 = 26. Pickets = 1200 in / 5.75 in = 209 pickets. Concrete per post: π × 5² × 24 − 16 × 24 = 1885 − 384 = 1501 in³ = 0.87 ft³. Total: 14 × 0.87 = 12.2 ft³ ÷ 0.6 = 21 × 80 lb bags.

Set posts below your local frost line — typically 24″–36″ in the northern US, 36″–48″ in the northern Midwest. Tamp 4–6 inches of gravel under each post for drainage, then fill with concrete. For higher fences or windy sites, use 6×6 posts and 24″ wide holes. The calculator's defaults are good for typical 6-ft privacy fencing in temperate climates.

FAQ

How deep should fence post holes be?
At least one-third of the post height above grade, and always below the local frost line. For a 6-ft fence in frost climate, 30–36″ deep is typical. Check your local code.
How many concrete bags per post?
For a 4×4 post in a 10″ × 24″ hole, about 1.5 × 80 lb bags. For a 6×6 post in a 12″ × 36″ hole, ~3 × 80 lb bags. The calculator returns the total for the whole fence.
What is the right picket gap?
Zero for shadow-box and board-on-board (privacy). 1/4″ to 1/2″ for a standard "privacy with airflow" picket fence. Up to 1.5″ for a decorative picket / spaced-board look.
How many rails do I need?
Two rails for fences up to 4 ft tall. Three rails for 5–6 ft. Four for 7–8 ft. The calculator multiplies your rails-per-section setting by the section count.
Does this calculator include gates?
No. Add the gate, hinge, and latch hardware separately. Allow for an extra-strong post on each side of any gate opening.
Is the calculator free?
Yes — free, no signup, runs in your browser.