Fence Material Calculator: Posts, Rails and Pickets

Calculate fence materials by entering the fence’s total length, post spacing, fence height, and picket width and gap. The calculator estimates the number of posts, rails, and pickets, plus the total rail length and picket coverage; adjust the results for gates, corners, and your chosen layout.

Formula

For a straight fence run with evenly spaced posts and regularly spaced pickets, the estimates are:

• Interior line posts: posts = ceiling(fence length ÷ post spacing) − 1.
• Total rail length: rail length = fence length × rails per section.
• Pickets: pickets = ceiling(fence length in inches ÷ (picket width + gap)).

Here, fence length is the run in feet, post spacing is the planned distance between posts in feet, rails per section is a count, and picket width and gap are inches. The ceiling function rounds a result up to the next whole item. The post result is for interior line posts; it does not include posts at the two ends, corners, or gates.

Worked Example

Using the calculator’s default values: a 100-foot straight run, 8-foot post spacing, 6-foot fence height, three rails per section, 5.5-inch pickets, and a 0.5-inch gap:

1. Line posts: ceiling(100 ÷ 8) − 1 = ceiling(12.5) − 1 = 12 interior line posts.
2. Rail length: 100 × 3 = 300 feet of rail.
3. Pickets: ceiling((100 × 12) ÷ (5.5 + 0.5)) = ceiling(1,200 ÷ 6) = 200 pickets.

The picket count is an approximate layout count, not a guarantee that every board will fit without trimming. The post figure is specifically the number of interior line posts under the formula; plan end and corner posts separately.

How to Plan the Fence Layout

Measure the fence path, not just the distance between the two farthest points. Walk the proposed line and record each straight run, corner, change in direction, and gate opening. For an irregular perimeter, calculate each straight run separately, then combine material totals. A single calculation over the perimeter can miscount posts because corners and gates change where sections begin and end.

• Mark gate openings and subtract their widths from the fence length used for rails and pickets.
• Count gate posts and corner or terminal posts separately. They may need different dimensions or hardware from ordinary line posts.
• Choose post spacing based on the fence system, rail lengths, ground conditions, and manufacturer’s installation guidance. The 8-foot default is only an example, not a universal requirement.
• Check whether the selected fence design needs two, three, or another number of rails. Taller or heavier designs may call for a different arrangement.

A fence height of 6 feet is included as a useful reference for this example, but height does not change these three material totals directly. It matters when selecting the actual post, rail, and picket lengths and when determining how much of each post must extend into the ground.

Turn Estimates into a Materials List

Calculator totals describe quantities, while a shopping list must account for available stock lengths and the build details. For example, 300 feet of rails does not necessarily mean buying three 100-foot pieces. Rails are typically installed as individual spans between posts, so determine the span dimensions and cut plan before deciding how many boards to buy.

• Posts: add the two end posts, corner posts, and any gate posts to the interior line-post estimate. Replace the simple estimate with a section-by-section count when runs meet at corners or contain openings.
• Rails: calculate the number of rail spans in each section and choose stock lengths that can be cut to fit. Allow for the actual connection method and any required overlap.
• Pickets: verify the intended spacing with a short sample layout. Board widths can vary, and a fence may require a narrower final picket or a small adjustment to gaps.
• Hardware: make a separate list for fasteners, brackets, gate hardware, caps, and concrete or other post-setting materials, as applicable to the design.

It is sensible to allow for a modest number of spare boards or fasteners when ordering, especially if cuts, defects, or future repairs are a concern. The right allowance depends on stock quality and the complexity of the layout; it is not a fixed percentage supplied by this calculator.

Common Counting Errors and Limits

The line-post formula assumes one uninterrupted straight run, evenly spaced posts, and a desired maximum spacing. When the length does not divide evenly by the spacing, the formula counts enough sections to keep the spacing at or below the entered value. For the 100-foot example, 13 sections would average about 7.69 feet, with 12 interior posts between the two ends. Actual placement may require adjusting individual spans.

The picket formula treats the repeat distance as picket width plus gap. That estimates a repeating layout along the full length; it does not explicitly account for whether the first and last pickets sit flush with the ends, gaps at boundaries, or special corner details. Picket width and gap must use the same units. The calculator converts feet of fence to inches by multiplying by 12.

Do not confuse total rail length with the number of rail boards: the result is a length, while purchase quantities depend on stock lengths and cuts. Likewise, the post count is not a complete total until terminal, corner, and gate posts are included. The calculator also does not determine suitable post depth, structural sizing, or local requirements; use the fence system’s installation instructions and check relevant local rules before building.

Frequently Asked Questions

How many posts do I need for 100 feet of fence?
At 8-foot maximum spacing on one straight 100-foot run, the calculator estimates 12 interior line posts, plus two end posts. Corners and gates require separate posts, and actual spacing may be adjusted to suit the layout.

How do I calculate fence pickets?
Convert fence length to inches, then divide by picket width plus the planned gap and round up. For 100 feet with 5.5-inch pickets and 0.5-inch gaps, the estimate is 200 pickets.

How many rails does a fence need?
The number varies with fence height, construction, and the fence system’s design. Enter the planned rail count per section; do not treat the calculator’s default of three as a rule for every fence.

Does the calculator include gate and corner posts?
No. Its post output estimates interior line posts for a straight run and excludes terminal, corner, and gate posts. Count those from the actual layout.

Should I add extra fence materials?
A small reserve can help cover damaged boards, cut errors, or later repairs, but the amount depends on the project. First confirm measurements, openings, stock lengths, and the fence maker’s installation details.

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in l | Fence length | ft | 100 | 0
in s | Post spacing | ft | 8 | 0
in h | Fence height | ft | 6 | 0
in r | Rails per section | - | 3 | 0
in w | Picket width | in | 5.5 | 0
in g | Picket gap | in | 0.5 | 0
out posts | Line posts, before end-post adjustment | posts | ceil(l / s) - 1 | 0
out rails | Total rail length | ft | l * r | 0
out pickets | Pickets, approximate | pieces | ceil(l * 12 / (w + g)) | 0