Building a Fence: Calculating Panels, Posts, and Concrete Before You Buy
How to calculate fence panel count, post count, and footing concrete together for an accurate materials list.
A fence project's materials list comes down to three connected calculations — how many panels, how many posts, and how much concrete to set those posts — each depending on the previous one.
Step 1: panels from total fence length
Panels Needed = ceil(Total Length / Panel Width). A 120-foot fence run using 8-foot panels: ceil(120/8) = 15 panels.
Step 2: posts from panel count, not fence length directly
Posts Needed = Panels + 1. Following from step 1: 15 + 1 = 16 posts — not calculated independently from fence length, but derived directly from the panel count, since each panel needs a post at both ends and adjacent panels share a post between them.
Step 3: concrete for setting each post
Each post typically needs a footing — commonly estimated at around 0.67 cubic feet of concrete per standard post hole (roughly a 10-inch diameter, 30-inch deep hole, though local frost line depth requirements vary). For 16 posts: 16 × 0.67 ≈ 10.7 cubic feet, or roughly 10.7/27 ≈ 0.4 cubic yards of concrete — small enough that pre-mixed bags (rather than a ready-mix delivery) are usually the more practical choice for a project this size.
Why the post count, not the panel count, drives the concrete estimate
It's easy to mistakenly calculate concrete based on panel count instead of post count, understating the true need by one footing's worth of concrete. Since concrete goes into post holes, not panels, the post count (always one more than the panel count) is the correct multiplier.
If the fence includes a gate or stairs down a slope
A sloped yard sometimes calls for stepped sections or small stairs integrated into a fence or deck line — the same stair rise/run calculation used for interior staircases applies here too: total rise divided by a target step height gives the number of steps needed, which then determines how the actual rise per step adjusts to fit that whole number.
The complete materials sequence
Fence length → panel count → post count → concrete volume. Each step depends directly on the one before it, which is exactly why estimating out of order (like guessing concrete needs before finalizing post count) tends to produce the most common ordering mistakes on a DIY fence project.
Estimate your own project with the fence calculator, concrete calculator, and stair calculator.