How to Estimate a Fence: Posts, Rails, and Pickets

Start with accurate linear footage

Every fence takeoff begins with the total run measured in linear feet (LF) along the centerline of the fence. Walk the layout, measure each straight segment, and add them together. Pull your tape along the ground the posts will actually follow, not the property line on paper -- slopes, jogs around utilities, and setback offsets all change the real number. Measure gate openings separately and subtract them from the fenced run, because a 4-foot walk gate and a 10- or 12-foot drive gate need no infill pickets across the opening.

For a rectangular yard, the perimeter is simply two times length plus two times width. For irregular lots, break the run into straight legs, measure each, and sum. Round the total up to the nearest foot. This single figure -- total LF -- feeds every other quantity in the estimate, so it is worth measuring twice. On rough or sloped ground, a measuring wheel or a quick LiDAR scan of the perimeter is faster and less error-prone than a tape; ProBuildCalc can pull linear footage straight from a phone scan of the site so the takeoff starts from a measured plan instead of a sketch.

Count the posts

Posts are spaced on center, and the industry-standard maximum is 8 feet on center for most wood and many metal residential fences. Many contractors tighten that to 6 feet on center for stronger panels, heavier privacy fences, or windy sites. To get post count for a single straight run, divide the run length by your spacing and add one for the closing post: posts = (run LF / spacing) + 1. A 120-foot straight run at 8-foot spacing is 120 / 8 = 15 spaces, plus 1 = 16 posts.

For a continuous closed loop like a backyard perimeter, you do not add the extra post -- the start and end share a corner -- so posts roughly equal total LF divided by spacing. Then add posts the spacing math misses: one at every corner, one on each side of every gate, and one at any change in direction. Gate posts carry hinge load and should be the heaviest posts on the job, often a larger section or set deeper in concrete. A practical rule: count the line posts from the spacing formula, then physically add corner and gate posts by walking the plan.

Post length depends on fence height plus embedment. The common rule of thumb is to bury about one-third of the post, or a minimum of 24 to 30 inches below grade, whichever is greater, and below the local frost line in cold climates. A 6-foot-tall fence therefore wants an 8-foot post (6 feet above grade, 2 feet in the ground). For concrete-set posts, figure roughly one to two 50- to 60-pound bags of premixed concrete per hole for a standard 4x4 in a 8- to 10-inch-diameter hole; larger gate posts and wider holes use more.

Count the rails (stringers)

Rails, also called stringers or backer rails, are the horizontal members that span between posts and carry the pickets. The count is driven by fence height. Fences up to about 4 feet typically use 2 rails (top and bottom). Fences from roughly 5 to 6 feet use 3 rails (top, middle, bottom). Fences taller than 6 feet, or any fence that will see heavy wind or livestock, often use 4 rails.

To estimate rail material, multiply the total fence run by the number of rails: rail LF = total LF x rails per section. A 120-foot fence at 3 rails needs 360 linear feet of rail stock. If rails come in fixed lengths -- 8-foot rails are common and align with 8-foot post spacing -- divide the rail LF by the stock length to get a piece count, then add waste for cuts and unusable ends. With 8-foot post bays, one rail per bay per course makes the count clean: bays x rails per section equals the rail piece count, before waste.

Count the pickets

Pickets (also called boards or palings) are the vertical infill. The picket count depends on board width and whether you want a tight, gapped, or board-on-board look. The base formula is: pickets = (fenced LF x 12) / (picket width + gap), using inches. For a solid privacy fence with 5.5-inch-wide boards (a nominal 1x6) butted with no gap, that is 5.5 inches per picket; with a 0.5-inch gap it becomes 6 inches per picket.

Worked example: a 120-foot privacy fence (minus a 4-foot gate = 116 fenced feet) with 5.5-inch boards and no gap. 116 x 12 = 1,392 inches; divide by 5.5 = about 254 pickets. The same fence with a half-inch gap uses 6 inches per board: 1,392 / 6 = 232 pickets. Board-on-board, where boards overlap to hide gaps and account for shrinkage, increases the count by roughly 30 to 50 percent depending on overlap, so plan for it deliberately rather than discovering it at install. Spaced picket and shadowbox styles use the same formula with the chosen gap plugged in.

Always confirm actual milled width, not nominal. A 1x6 is really 5.5 inches and a 1x4 is really 3.5 inches; estimating off nominal 6- and 4-inch widths will leave you short on every run.

Add waste, hardware, and a final check

Add waste to every cut material. For pickets and rails, 10 percent is a reasonable allowance on straight, simple layouts; bump to 15 percent for fences with many corners, slopes, stepped sections, or where board grading will reject knotty stock. Posts generally do not get a percentage waste -- you order the exact count plus a spare or two for breakage. Round up to whole pieces and whole bags after applying waste.

Do not forget the fasteners and accessories, which are easy to leave off a bid. Budget screws or nails per picket (typically 2 per rail crossing, so a 3-rail fence is about 6 fasteners per picket), plus post caps, rail brackets or fasteners, gate hardware (hinges, latch, and often a drop rod or cane bolt for double gates), and concrete by the bag.

Close the estimate with a sanity check that ties back to your starting number. Posts should land near total LF divided by spacing plus your corner and gate adds; rail LF should equal total LF times rails per section; picket count should match fenced LF times 12 divided by your spacing-per-board. If any line item is wildly off those ratios, re-measure before you order -- a fence priced short almost always traces back to bad linear footage, not bad math.