The fence calculator above takes one fence run and returns the whole order: posts, rails, pickets or panels, bagged concrete for the post holes, and a total cost. It handles wood privacy, spaced picket, board-on-board, post-and-rail, vinyl panel and chain link from a single type selector, because all six are the same arithmetic with different spacing numbers plugged into it.
Arb Digital publishes this as part of a free construction estimating set. It is deliberately one page rather than a family of near-identical pages. A privacy fence and a picket fence differ by two inputs — the gap between boards and the number of rails — so splitting them into separate calculators would mean the same maths, duplicated, with a different heading. Change the type selector and every downstream number updates.
What This Fence Calculator Does
It counts four things and prices them. Posts come from the fence run divided by your maximum post spacing, rounded up, plus one closing post, plus one extra post per gate. Rails come from sections multiplied by rails per section. Pickets come from the pickable run — total length minus every gate opening — divided by the coverage width of one picket. Concrete comes from the volume of a cylindrical hole minus the volume of the post that sits in it, multiplied by the post count and divided by the yield printed on the bag.
It stops where a survey begins. The perimeter calculator is the right tool if you only need the distance around a shape and nothing else — that is the boundary between the two pages: perimeter returns a length, this returns a bill of materials. For the concrete side of the job in bulk rather than bags, our concrete calculator handles ready-mix volumes.
How to Use It
- Pick units and fence type. The type selector loads conventional starting values for rails, picket width, gap and post spacing. Nothing is locked — change any of them to match the product you are actually buying.
- Enter the total run and the height. Add every leg of the fence together. If the fence turns corners, the corner posts are already counted, because a corner is just a post with fence on two sides.
- Set post spacing. Eight feet is the common wood-fence figure because rails are sold in eight-foot lengths. Chain link commonly runs wider. Your product's instructions and local wind loading govern the real limit.
- Enter gates. Gate openings are removed from the picket run and each gate adds a post, since a gate needs a hinge post and a latch post rather than one shared line post.
- Set hole size, bag yield and waste. Hole depth follows your local frost line. Bag yield is printed on the bag. Ten percent waste is a starting point for a straight run on flat ground.
The Formula / How It's Calculated
Five formulas run in order. Sections = ceil(run ÷ maximum spacing), and posts = sections + 1 + gates. Actual spacing then becomes run ÷ sections, which is almost always a little under your maximum — that is correct and intended, because the maximum is a limit, not a target. Rails = sections × rails per section.
Pickets use a coverage width: coverage = picket width + gap, where a negative gap represents the overlap on a board-on-board fence. Raw pickets = pickable run ÷ coverage, and pickets to buy = ceil(raw × (1 + waste)). Concrete per hole is the cylinder volume minus the buried post: π × (hole diameter ÷ 2)² × depth − (post width² × depth). Total bags is that figure times the post count, divided by bag yield, rounded up.
Two of those inputs are governed by things outside arithmetic. Post depth is set by the frost depth in your jurisdiction, and preservative retention for buried timber is set by the American Wood Protection Association Use Category System — ground-contact fence posts fall under UC4A, described in the USDA Forest Service Guidelines for Selection and Use of Pressure-Treated Wood.
Why One Page Replaces Ten Fence Calculators
Search for fencing quantities and you will find separate pages for privacy fences, picket fences, board-on-board fences, split-rail fences, vinyl fences, chain link, wire mesh, and several more. Open three of them and the inputs are the same. The reason the split exists is that a page per keyword ranks for a page per keyword, not because the mathematics differs.
The differences are genuinely small, and they live in three variables. Rails per section: two for a low picket fence, three for a six-foot privacy fence, one top rail for chain link, two or three for ranch rail. Coverage width: a solid privacy fence has zero gap, a picket fence typically has a gap close to the picket width, and board-on-board has a negative gap because each board laps the one behind it. Post spacing: wood fences follow the rail stock length, chain link runs wider because the fabric spans between posts rather than sitting on rails.
Set those three and the fence type is fully described. That is why the selector exists and why the fields stay editable underneath it — a preset that you cannot override is worse than no preset, because it hides the assumption instead of showing it to you.
Board-on-Board Is the One People Get Wrong
A board-on-board fence looks like a privacy fence with extra boards, and estimating it like a privacy fence is the single most expensive mistake in this list. Each board overlaps its neighbour, so the run each board covers is less than the board is wide. With 5.5 inch boards and a 1 inch overlap, one board covers 4.5 inches of fence, not 5.5 — which is 22 percent more boards over the same run.
The calculator handles this through a negative gap. Enter −1 for a one-inch overlap and the coverage width drops to 4.5 inches automatically. The reason the fence is built this way is that boards shrink as they dry; a solid butted fence develops daylight gaps within a season, while an overlapped fence stays visually solid because the overlap absorbs the shrinkage. If you want privacy that survives the first summer, that extra 22 percent is the price of it.
Post Depth, Frost and the Concrete Number
The concrete figure moves faster than people expect, because hole volume scales with the square of the diameter. Widening a hole from 10 inches to 12 inches is a 44 percent increase in concrete for the same depth. Going deeper is linear by comparison — 30 inches to 36 inches is a 20 percent increase. If your bag count looks high, the diameter is usually the reason, not the depth.
Depth itself is not a preference. In cold climates a post set above the frost line will be lifted by frost heave, and a fence that has heaved does not settle back level. Frost depth is a local figure published by your building department and it varies enormously across a single country. A common rule of thumb is to bury one third of the post's total length, but where the frost line is deeper than that, the frost line wins. This tool does not choose a depth for you and cannot — enter the depth your jurisdiction requires.
One more detail on the volume: the calculator subtracts the post from the hole, which most quick estimates skip. On a 10 inch hole with a 3.5 inch square post, the post displaces about 16 percent of the hole. Over 14 posts that is roughly four bags of concrete you would otherwise have bought and carried home for nothing.
Slope, Corners and the Length You Actually Measured
Fence length is measured along the ground, and on sloping ground that is longer than the distance on a plan. If you are working from a site plan or a plot survey, the figure printed there is the horizontal distance. On a 10 percent grade the ground distance is about half a percent longer, which is negligible; on a steep 30 percent bank it is over four percent, which is not.
How the fence follows that slope changes the picket count too. A racked fence, where the pickets stay vertical and the rails tilt with the ground, needs the same pickets as a flat run of the same ground length. A stepped fence, where each section stays level and drops at the post, needs longer pickets on the downhill side of every section — often significantly longer at the bottom of a long slope. The slope calculator converts a rise and run into a grade if you need to check what you are dealing with, and the roof pitch calculator covers the same conversion in builder's rise-over-run terms.
Reading the Raw Count Against the Purchasable Count
Every quantity here is shown twice: the honest requirement, and the number you can put on an order. A 100 foot privacy fence with one four-foot gate needs 209.5 pickets by measurement. You cannot buy 209.5, and buying 210 leaves you with no allowance for a split board, a bowed board you reject on sight, or the two you cut short. With 10 percent waste the order is 231, and the 21 spare pickets are the entire buffer between finishing the fence and making a second trip.
Waste is not padding for its own sake. On a straight run over flat ground, 10 percent is comfortable. Add several corners and the offcuts multiply, because the last picket in each section is often ripped narrower to close the gap cleanly at the post. On a stepped fence over a slope, every step produces an angled cut. Fifteen percent is a more realistic figure for either of those, and the field is editable so you can decide rather than accept a hidden default.
Costing the Fence Beyond Posts and Pickets
The cost line covers posts, rails and pickets, because those three scale directly with the dimensions you entered. A complete fence budget also carries concrete, fasteners, gate hardware, post caps, and any finish. Gate hardware in particular is a fixed cost per gate that does not scale with fence length at all, and on a short run it can be a surprising share of the total.
Fasteners for a privacy fence are worth counting properly: each picket is typically fixed at every rail it crosses, so a 241-picket fence with three rails needs well over a thousand nails or screws. As with any preservative-treated timber, the fixings have to be rated for it — the copper-based preservatives in modern treated wood corrode plain steel, and the USDA Forest Service publication Protecting Wood Fences for Yard and Garden covers the decay and finishing side of the same problem. For span and framing guidance on any structural timber in the job, the American Wood Council publishes the design documents that prescriptive tables are built on.
Arb Digital builds free calculators and interactive tools that earn search traffic for trade and construction businesses. Browse the full library, or tell us what your customers keep asking you to work out.
Browse Free Tools Talk To Arb DigitalCommon Mistakes to Avoid
- Forgetting the closing post — a run divided into sections always needs one more post than sections, and each gate adds another on top.
- Estimating board-on-board at full board width — the overlap reduces coverage, and ignoring it under-orders the fence by roughly a fifth.
- Not subtracting the post from the hole — the buried post displaces a real share of the concrete you would otherwise buy.
- Setting posts above the frost line — frost heave lifts shallow posts permanently, and no amount of concrete compensates for a hole that is too shallow.
- Using plain steel fixings on treated timber — modern preservatives are corrosive to uncoated steel, and the fence fails at the fixings long before the wood.
Related Free Tools From Arb Digital
Pair this with the concrete calculator for bulk post-hole concrete, the gravel calculator if you are laying a gravel drainage layer at the post bases, the perimeter calculator to measure the run around an irregular plot, and the cubic yard calculator to convert any bulk volume into ordering units. The free online tools hub lists every calculator we publish.
Frequently Asked Questions
At eight foot maximum spacing a 100 foot run divides into 13 sections, so it needs 14 posts plus one extra for each gate. The actual spacing works out at 7.69 feet, which is under the maximum — that is correct, because the maximum is a limit rather than a target.
With 5.5 inch pickets butted with no gap and a four foot gate removed from the run, the pickable length is 96 feet, which needs 209.5 pickets by measurement and 231 with a 10 percent waste factor. Change the gap and that number moves immediately.
A 10 inch diameter hole 30 inches deep holds about 1.36 cubic feet, and a 3.5 inch square post displaces about 0.21 of that, leaving roughly 1.15 cubic feet of concrete per hole. At a 0.6 cubic foot bag yield that is two bags per post.
Deep enough to clear your local frost line, which is a figure published by your building department and varies widely by region. A common rule of thumb is one third of the post's total length, but where the frost line is deeper than that, the frost line governs.
Yes. Enter a negative number in the gap field to represent the overlap. A 5.5 inch board with a one inch overlap covers 4.5 inches of fence, and the calculator raises the picket count accordingly.
Yes. Choose the type from the selector. Chain link uses a single top rail and wider post spacing, and vinyl uses whole panels rather than individual pickets, so the picket figure is read as a panel count instead.
The decimal is the honest measurement of what the fence needs. The whole number is what you can actually buy after the waste factor is applied and the result is rounded up. The gap between the two is your spare stock.
No. It counts what you specify. Post size, spacing limits, embedment depth and wind loading are governed by your local building code and the fence manufacturer's instructions, and a licensed professional should confirm them before you build.
This tool produces material estimates only. Post embedment, spacing, height limits and wind loading are governed by your local building code and must be confirmed by a licensed professional before construction.
