Round pen calculator

Zero or negative diameter is rejected as invalid_input instead of a hollow zero-radius pen that no builder can erect. Use it free in the browser before you buy, or call the API at $0.002 per successful request when estimating software needs a reproducible take-off.

How circumference and panel count are computed from diameter

Circumference equals π times that diameter: C = π × diameter. Each panel contributes panel_length along the perimeter, so the exact (generally non-integer) panel count is circumference divided by panel_length. Builders cannot order a fraction of a welded panel, so the published count is the ceiling of that ratio: panels = ceil(π × diameter / panel_length). Diameter and panel_length must use the same length unit because the calculator never converts feet to metres. Diameter must be strictly positive: a zero-diameter pen has no interior, and a negative diameter has no physical meaning, so both cases return invalid_input naming diameter. The response echoes rounded inputs, radius as half the diameter, circumference, exact_panels before ceiling, the integer panels to order, covered_length as panels times panel_length, overhang as covered_length minus circumference, a short English message, and ordered substitution steps you can paste into a quote.

How to call the API and what comes back

String forms of numbers are accepted when they match a strict finite numeric pattern; prefer sending numbers when you control the client, and avoid unit suffixes or thousand separators that would fail that pattern. Keep metres with metres or feet with feet: mixing centimetres for the panel and metres for the pen would silently produce a wrong count. Send a JSON body with two required fields: diameter (aliases D, d, dia, pen_diameter, inside_diameter) and panel_length (aliases panel, panel_len, L, length, panel_size, panel_width). Both must be finite strictly positive numbers within the published absolute range so the circumference and the panel count remain finite in IEEE double precision on the Worker and in the browser. On success the response sets radius to diameter over two, circumference to π times diameter, exact_panels to the unrounded ratio, panels to the ceiling of that ratio, covered_length to panels times panel_length, overhang to the extra full-panel cover after the circumference is met, formula to the circumference and panels expressions, message to a short English summary, and steps to an ordered substitution log. Failed validation—missing fields, non-finite numbers, zero or negative diameter, non-positive panel_length, 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 a classic fifty-by-twelve case with a sixty-by-twelve case that also exercises the ceiling, and include a deliberate zero or negative diameter to prove the invalid_input path in your own tests. Nothing is stored after the response returns, and the work never leaves your isolate for a model or a network hop.

Practical sizes, limits, and related searches

Measure the inside diameter you actually want to work in—not the outside of the posts—and choose a panel_length that matches your product SKU. Ten-foot, twelve-foot, and sixteen-foot livestock panels are common in North America; two-metre and three-metre sections are common elsewhere, but the tool accepts any positive pair of diameter and panel_length in the same unit. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when you deliberately send a zero diameter to verify error handling. On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002.