Fence panel calculator

Zero or negative panel width is rejected with a clear invalid_input error instead of inventing infinite panels, and non-positive length is rejected the same way.

How fence panels and posts are counted from length and panel width

A straight fence run of positive length is covered by modular panel sections whose nominal width is panel_width along the line. Effective length equals the measured length times one plus waste_factor; waste_factor defaults to zero when omitted and may be set between zero and one when you want a fractional cushion for cuts, damage, or fitting. Length and panel_width must use the same length unit—metres with metres, feet with feet—because the calculator never converts units and only needs the dimensionless ratio. Panel width must be strictly positive: zero width would imply infinitely many panels, and negative width has no physical meaning on a line, so both cases return invalid_input. The response also reports covered_length as panels times panel_width, last_section_width as the residual bay when fitting the measured run (useful when the last panel is cut to length), and overhang as how much extra full-panel cover remains after the effective length is met.

How to call the API and what comes back

Prefer sending numbers rather than pre-formatted strings when you control the client; when you must send strings, avoid unit suffixes or thousand separators that would fail the finite-number pattern. Send a JSON body with two required fields: length (aliases fence_length, L, len, run, run_length, total_length) and panel_width (aliases panel_section_width, section_width, width, W, panel_w). Optionally send waste_factor (aliases waste, waste_pct, allowance, spoilage); when omitted it defaults to zero. Length and panel_width must be finite positive numbers within the published absolute range so the ratio and counts remain finite in IEEE double precision on the Worker and in the browser. waste_factor when provided must be a finite number between zero and one inclusive; string forms of numbers are accepted when they match a strict finite numeric pattern. On success the response sets effective_length, panels to the section count, posts to panels plus one, covered_length, last_section_width, overhang, formula to the panels and posts expressions, message to a short English summary, and steps to an ordered substitution log. Failed validation—missing fields, non-finite numbers, zero or negative panel_width, non-positive length, waste_factor outside zero to one, or values outside absolute limits—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item. Pair exact multiples (for example length forty-eight and panel_width eight) with a non-exact case that exercises the ceiling, and include a deliberate zero or negative panel_width to prove the invalid_input path in your own tests.

Practical tips, limits, and related searches

Keep dimensions inside the published absolute range so counts cannot overflow into non-finite results the solver must reject. Prefer this capability when you already know the run length and modular panel width and only need integer material counts; if your source is a closed perimeter, call once per straight side and sum posts carefully so shared corner posts are not double-counted. Measure the clear run along the fence line and choose a panel_width that matches your product SKU—six feet, eight feet, and two-metre sections are common, but the tool accepts any positive pair of length and panel_width in the same unit. If the last bay would be awkwardly short, either adjust the overall run, pick a different panel product, accept the ceiling rule and cut the last panel to fit, or set a modest waste_factor when ordering spare stock; this calculator always covers the full effective length with ceil. When teaching or writing tests, pair an exact multiple with a non-exact case and a zero panel_width rejection. This landing targets people searching for a fence panel calculator, how many fence panels do I need, fence panels and posts from length, or panel section material list online; it is not a picket-board gap calculator, not a post-spacing rails estimator, not a concrete post-hole volume tool, and not a multi-segment property survey that places posts at GPS coordinates. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when you deliberately send zero panel width to verify error handling. Round-trip checks are easy: recompute ceil of effective length over panel_width by hand, add one for posts, and confirm the published integers match.