Conversion calculator

Which units convert, and how the SI hub works

Every conversion multiplies the input by how many SI-hub units equal one source unit, then divides by how many SI-hub units equal one target unit: result equals value times to_si of from over to_si of to. Common aliases such as inches, pounds, litres, and kWh are accepted case-insensitively and canonicalized in the response so tests stay stable.

Input contract, response shape, and error behaviour

Value must be a finite number or a strict numeric string whose absolute magnitude does not exceed one trillion. A kilogram-to-metre request is an unsupported unit pair, not a silent dimensionless ratio. Same-unit requests succeed and return the input magnitude with a short note that no change of unit was required. Wire this into catalogs, mobile clients, or batch jobs that already hold a reading and only need a second unit for display or a standards table without shipping a conversion spreadsheet in every binary. Send a JSON body with three required fields: value (aliases amount, quantity, and v), from (aliases from_unit, unit_from, and source), and to (aliases to_unit, unit_to, and target). From and to must resolve to supported unit names after alias normalization, and they must share a measurement kind. On success the response echoes the rounded input value, canonical from and to labels, kind as length mass volume time area or energy, result as the converted magnitude, factor as the exact from-to multiplier, si_unit and si_value as the hub intermediate, formula as the short equation string, message as an English summary, and supported_units as the canonical labels of that kind. Failed validation is never charged: missing fields, non-finite numbers, values outside absolute limits, unknown unit names, and mixed-kind pairs all return invalid_input with a message that names the problem. Pricing is a flat $0.002 per successful request with unit item.

Practical tips, limits, and when to use this landing

Round-trip checks are straightforward: convert A to B and B back to A and confirm you recover the original within the published twelve-decimal rounding. Classic checks include two point five four centimetres to one inch, one mile to one point six zero nine three four four kilometres, one pound to zero point four five three five nine two three seven kilograms, and one US gallon to three point seven eight five four one one seven eight four litres. Prefer sending bare JSON numbers for value when you control the client; string numbers are accepted only when they match a strict finite numeric pattern without currency symbols, thousand separators, or unit suffixes. Normalize display labels on your side if you need locale-specific spellings—this API always returns the short canonical tokens such as cm, in, kg, L, gal, min, ft2, and kWh so automated tests stay byte-stable. Stay inside the absolute range so intermediate SI products cannot overflow IEEE double precision on the Worker or in the browser. This landing targets people searching for a conversion calculator that turns one named unit into another of the same kind with published factors; it is not a temperature converter, not a live currency converter, not a single-pair centimetre-to-inch microsite, and not a general spreadsheet formula engine. Prefer this capability when both endpoints sit in the supported table and you need deterministic factors plus an SI audit trail; if you only need to reformat a number for a locale without changing physical unit, use a number-format tool instead. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when clients deliberately probe mixed kinds or unknown names.