Methodology

This page explains how the FencingCalcs calculators are derived and verified — and why they need no ongoing maintenance to stay correct.

1. Timeless math, stable conventions

Every tool computes from a closed-form formula: posts = ceil(line ÷ spacing) + 1 (+ gate/end/corner); sections = ceil(line ÷ spacing); rails = sections × rails per section; pickets = ceil(line × 12 ÷ (width + gap)); panels = ceil(line ÷ panel width); concrete bags per post = ceil((π·r²·h − post) ÷ bag yield); stain gallons = face area ÷ coverage × coats; cost = (quantity × your $/unit + labor + add-ons − discount) ×(1 + contingency); and cost-to-fence-an-acre derives the perimeter from the area (a square is the minimum-perimeter shape) or from your length and width. The only baked-in numbers are stable identities (1 acre = 43,560 ft², 1 rod = 16.5 ft, ceil for whole bags/panels, hole volume = π·r²·h) and labeled industry planning typicals (post spacing, panel/picket widths, post depth, bag yields, coverage, waste %). These do not drift, so the statements stay true over time.

2. No prices, no feeds

There is deliberately no material or labor price, no regional cost index, no product catalog, no contractor directory and no live rate. Every cost tool works on the prices you enter from your own quotes and bills ($/linear ft, $/post, $/panel, $/gate, labor $, tear-out $, $/gal stain, $/ft wire). Labeled cost bands are shown only as a sanity guide. That is why the site is correct regardless of what fence or labor prices do.

3. The board-on-board & post-hole-volume derivations

Board-on-board and shadowbox fences overlap each board, so the coverage per board is width − overlap and the count is ceil(line × 12 ÷ coverage) — about a third more boards than a butted fence. The concrete-per-post tool takes the cylindrical hole volume π × (diameter ÷ 2)² × depth, subtracts the square post that occupies it, and divides by the labeled bag yield, rounding up to whole bags. We publish the labeled yields and let you confirm them against your product’s bag.

4. Numeric self-check

Every formula is asserted against a worked example with known numbers (for instance: a 200 ft fence at 8 ft spacing is 26 posts, 25 sections and 75 rails; 100 ft of 3.5" pickets at a 1.75" gap is 229 pickets; a 10"×30" hole around a 4×4 post takes 3 bags of 60 lb concrete; a 150 ft vinyl fence at $30/lf plus a gate at 10% contingency is about $5,335; fencing an acre at $25/lf is about $20,875). A release gate runs all of these and fails on any mismatch, so “verification” here is mathematical correctness plus accurate conventions — not a time-based check.

5. Estimate or quantity guide, not a bid or a design

The contingency %, waste %, post spacing, rails per section, picket width & gap, panel width, hole diameter & depth, bag yield and stain coverage are labeled planning typicals — a starting point, not a spec. Every result is a planning estimate or a material-quantity guide: get itemized written quotes from licensed, insured fencing contractors, confirm panel/picket dimensions and bag yield against your product, and order a little extra (~10%) for waste, corners and terrain. A post depth or footing value is a labeled typical + a concrete bag quantity, not a structural or geotechnical design; a boundary is for a surveyor and local ordinance. Call 811 to locate utilities before you dig. Nothing here is an install procedure, an engineering determination, or property-law advice.