How to use the fence calculator
- Enter the Total fence length, Post spacing and Fence height.
- Choose Rails per section and a Fence style (pickets or posts and rails only).
- For pickets, enter the Picket width and Gap between pickets (0 for privacy).
- Enter the Post hole diameter and Post hole depth, and choose a Concrete bag size.
- Optionally add prices for posts, rails, pickets and concrete.
How it works
The calculator assumes a straight run of 4×4 posts (3.5 in square) and subtracts the post from each hole’s concrete volume. Bags per post are rounded up using typical premixed bag yields: 0.30 ft³ for 40 lb, 0.375 ft³ for 50 lb, 0.45 ft³ for 60 lb and 0.60 ft³ for 80 lb.
Minimum post length is the fence height plus the hole depth. Add a post for each gate and at every corner or end that does not fall on the spacing.
Sections = fence length ÷ post spacing, rounded up; posts = sections + 1
Rails = sections × rails per section
Pickets = fence length (in) ÷ (picket width + gap) × (1 + extra %), rounded up
Concrete per post = (π × (hole diameter ÷ 2)² − 3.5 in post²) × hole depth
Worked example
With the default inputs, a 100 ft fence with 8 ft spacing has 13 sections and 14 posts. Three rails per section gives 39 rails.
5.5 in pickets with no gap need 1,200 ÷ 5.5 = 218.2, or 229.1 with 5% extra, so 230 pickets. Each 10 in × 2 ft hole holds 0.92 ft³ of concrete, which is 3 bags of 50 lb, or 42 bags for 14 posts. Posts should be at least 8 ft long.
Tips before you buy
- Call 811 before digging so buried utilities can be marked.
- Set post holes below your local frost line; your building department can tell you the depth.
- Confirm property lines and check local rules and any HOA rules on fence height and setbacks before you build.
- Use posts rated for ground contact, and slope the concrete top away from the post to shed water.
Frequently asked questions
How many posts do I need for a 100 ft fence?
At 8 ft spacing, a straight 100 ft run has 13 sections and needs 14 posts. Add posts for gates and any extra corners.
How many bags of concrete per fence post?
For a 10 in hole 2 ft deep around a 4×4 post, about 0.92 ft³: three 50 lb bags or two 80 lb bags.
How deep should fence posts be?
A common rule is about one-third of the post’s above-ground height and below the frost line. For a 6 ft fence that means at least 2 ft, so an 8 ft post. Check local code.
How many pickets do I need for a fence?
Divide the fence length in inches by picket width plus gap, then add extra. A 100 ft privacy fence with 5.5 in pickets needs about 230 with 5% extra.
How many rails does a fence need?
Two rails for fences up to about 4 ft, three for 5–6 ft and four for fences over 6 ft.
Results are estimates based on the measurements you enter and typical material properties. Products vary, so check quantities with your supplier and follow product labels and your local building codes. Read the full disclaimer. Last reviewed October 9, 2026.