Start with the fence layout
Before ordering materials, measure the total fence run and identify gates, corners, ends, and changes in direction. A simple straight run is easier to estimate than a yard with several sections, so split a complex layout into measurable runs.
Calculate fence sections and posts
For a straight run, divide the fence length by the maximum post spacing you plan to use and round the number of sections up to a whole section.
Sections = ceiling(fence length ÷ post spacing)
Line posts = sections + 1
For example, a 100 ft straight run with an 8 ft maximum spacing needs 13 sections and 14 posts. The resulting average spacing is about 7.69 ft, so it does not exceed the 8 ft target.
Use the Fence Post Spacing Calculator to check this calculation.
Account for gates, corners, and ends
A basic straight-run calculation does not fully describe a real fence. Gates normally require their own posts and hardware. Corners and changes in direction can also require special posts. Count these separately from the simple line-post estimate and follow the fence system manufacturer's layout requirements.
Estimate rails
If each fence section uses a fixed number of rails, multiply the number of sections by the rails per section.
Total rails = sections × rails per section
For a 13-section layout using 3 rails per section, the planning quantity is 39 rail pieces before considering cuts, end conditions, or the available stock lengths.
Estimate pickets or boards
For a board or picket fence, the quantity depends on the exposed width of each board and the gap or overlap. Measure the actual face width rather than relying only on a nominal lumber size, then account for the chosen layout and waste.
For board-on-board or other overlapping styles, the visible coverage per board is smaller than the physical board width, so a simple board-width calculation can undercount the material.
Estimate post-hole concrete
Concrete quantity depends on the number of posts and the dimensions of each hole. A cylindrical planning estimate uses:
Hole volume = π × radius² × depth
Total concrete = hole volume × number of posts
The actual amount can be lower when the post displaces concrete inside the hole, while excavation variation and spillage can increase the amount purchased. Check the concrete product's stated yield before ordering bags.
Use the Fence Post Concrete Calculator for the hole-volume and bag estimate.
Worked example
Suppose a straight fence run is 100 ft, the target post spacing is 8 ft, and the design uses 3 rails per section.
- Sections: ceiling(100 ÷ 8) = 13
- Line posts: 13 + 1 = 14
- Rails: 13 × 3 = 39 rail pieces
- Average post spacing: 100 ÷ 13 ≈ 7.69 ft
This is a planning estimate. If the layout includes a gate or corners, add the required special posts and adjust the material takeoff for the actual design.
Common ordering mistakes
- Using the exact division result instead of rounding sections up.
- Forgetting gate, corner, end, or terminal posts.
- Using nominal board width when actual coverage width is different.
- Ignoring board or rail stock lengths and the cuts they create.
- Ordering concrete from a generic bag-yield assumption without checking the product label.
Frequently asked questions
How many fence posts do I need for 100 feet?
At an 8 ft maximum spacing on a straight run, 100 ft requires 13 sections and 14 line/end posts before adding special gate or corner posts.
How far apart should fence posts be?
The appropriate spacing depends on the fence system, material, height, loads, terrain, and manufacturer or local requirements. Use the maximum spacing allowed by the specific system rather than treating one spacing as universal.
How do I calculate fence rails?
Multiply the number of fence sections by the number of rails used in each section, then account for stock lengths and cuts.
How much concrete do fence posts need?
Estimate each cylindrical hole's volume, multiply by the number of posts, and then convert the total volume using the yield printed on the concrete product.
Should I add waste?
Yes. The appropriate allowance depends on the fence style, cuts, damage, layout complexity, and material. Gates and irregular sections should be handled separately.
Related calculators
Fence Calculator · Fence Post Spacing Calculator · Fence Post Concrete Calculator
Disclaimer: Estimates are for planning purposes only. Actual material requirements may vary based on site conditions, material specifications, installation methods, waste, and local requirements. Always verify quantities with your supplier or qualified professional before purchasing materials.