How this instrument works
A privacy fence is built differently from a picket fence in one important way: its boards butt tight against each other with no gap, since the whole point is blocking the view through rather than letting light and air pass between evenly spaced pickets. That distinction matters for the math — this instrument's board count assumes zero gap between boards, deliberately different from this site's own fence picket instrument, which spaces pickets apart by a chosen gap width.
Three separate quantities come out of the same few inputs. Boards needed divides the fence's total length (in inches) by each board's width, rounded up, since boards are butted with no gap to account for. Posts needed uses the standard 'count plus one' pattern — a post at each end of every span, shared between adjacent spans — giving ceil(length ÷ spacing) + 1. Rails needed multiplies the number of post-to-post spans by however many horizontal rails run in each section, since every section of fence between two posts carries its own full set of rails.
Rails per section is a disclosed, typical figure — most privacy fences use two to three horizontal rails depending on the fence's height and the panel's expected wind load, not a fixed universal number, so adjust it to match your own design or local practice. This is a materials-quantity estimate for boards, posts and rails only; it doesn't size post depth, footing, or account for a gate opening, which should be planned and subtracted separately.
- Enter Fence length (ft) — the total run of fence to be built.
- Enter Board width (in) — the actual width of each privacy board, butted tight with no gap.
- Enter Post spacing (ft) — the on-center distance between fence posts.
- Enter Rails per section — typically 2 to 3 depending on fence height; adjust to your own design.
- Read Boards needed, Posts needed and Rails needed beneath the inputs, all rounded up to whole units.
Worked example — a 100 ft privacy fence, 8 ft post spacing
Enter 100 into Fence length (ft), 5.5 into Board width (in), 8 into Post spacing (ft), and 3 into Rails per section. Boards needed: 100 ft is 1,200 inches, so ceil(1,200 ÷ 5.5) = ceil(218.18) = 219 boards, butted tight with no gap between them.
Posts needed: ceil(100 ÷ 8) + 1 = 13 + 1 = 14 posts, one at each end of every 8 ft span, shared between neighboring spans. Rails needed: (14 − 1) × 3 = 39 rails, three horizontal rails running the length of each of the 13 spans between those 14 posts.
Questions
How is this different from the site's fence picket instrument?
The picket instrument spaces individual pickets apart by a chosen gap width, matching an open-style picket fence where light and view pass between boards. This privacy-fence instrument assumes boards are butted directly against each other with zero gap, matching how a genuine privacy fence is actually built to block sightlines — the two use different board-count formulas because the fence styles themselves are built differently.
How many rails does my privacy fence actually need?
It depends mainly on fence height and expected wind load — a shorter fence (around 4 ft) commonly gets by with 2 rails, while a taller 6 to 8 ft privacy fence more often uses 3 rails for added rigidity against wind pressure across that larger solid panel area. This is a typical, commonly used range rather than a fixed code requirement, so check local practice or a manufacturer's own span tables if your design needs to meet a specific wind rating.
Why do posts get a '+1' added to the count?
Because a run needs one more post than it has spans — a single 8 ft span needs a post at each end, which is 2 posts for 1 span, and each additional span shares one post with its neighbor rather than needing two new ones. The ceil(length ÷ spacing) + 1 formula captures that pattern for any fence length and spacing.
Does this account for gates?
No — this instrument assumes a continuous run of fence with no openings. If your layout includes a gate, subtract the gate's width from the total fence length before entering it here, and plan the gate posts and hardware separately, since a gate opening changes both the board count and the post layout around it.
Should I buy extra boards beyond the calculated count?
A small overage is standard practice, since boards get cut to fit at corners or ends, and having a few spares on hand covers any warped, split, or otherwise unusable boards discovered during installation. This calculator returns the exact tight-fit count with no waste allowance built in, so add your own margin — often 5 to 10 percent — before placing a material order.