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Temperature Converter

Converts temperatures between Celsius, Fahrenheit, Kelvin and Rankine with the exact defining relations (°F = °C × 9/5 + 32, K = °C + 273.15, °R = °F + 459.67) and rejects values below absolute zero.

When to use

You need a weather, cooking, body or laboratory temperature in another scale, e.g. Fahrenheit to Celsius or Celsius to Kelvin.

Do not use when: You need to convert a temperature difference (a change of 10 °C is 18 °F, not 50 °F: multiply by 9/5 without the offset) or heat energy (use energy).

Formula

°F = °C × 9/5 + 32; °C = (°F − 32) × 5/9; K = °C + 273.15; °R = °F + 459.67 = K × 9/5

Kelvin is the base: the input is converted to kelvin and then to the target scale. Results below 0 K raise OUT_OF_RANGE.

Inputs

Parameter	Type	Required	Description
`value`	number	yes	Amount to convert, expressed in from_unit.
`from_unit`	enum: C \| F \| K \| R	yes	Unit of the input value. Accepted symbols: C, F, K, R; spelled-out names and common abbreviations are accepted too.
`to_unit`	enum: C \| F \| K \| R	yes	Unit to convert into (same symbols as from_unit).

Outputs

Output	Type	Description
`result`	number	Converted value expressed in to_unit (rounded to 6 decimals; see result_text for very small or very large values).
`result_text`	string	The conversion as text with 6 significant figures, e.g. "5 mi = 8.04672 km".
`formula`	string	Relation used, e.g. "1 mi = 1.609344 km".
`factor`	number	Multiplier from from_unit to to_unit (result = value × factor); absent for non-linear conversions.
`conversion_table`	object	The input value expressed in every supported temperature unit (6 significant figures), keyed by unit symbol.

Example

100 °F to °C: {"value":100,"from_unit":"F","to_unit":"C"} → {"result":37.777778,"formula":"°C = (°F − 32) × 5/9","result_text":"100 °F = 37.7778 °C","conversion_table":{"K":310.928,"R":559.67}}

25 °C to °F: {"value":25,"from_unit":"C","to_unit":"F"} → {"result":77,"formula":"°F = °C × 9/5 + 32","conversion_table":{"K":298.15,"R":536.67}}

GET https://tttkmbb.com/api/v1/calculate/temperature?value=100&from_unit=F&to_unit=C

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/temperature (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/temperature · Markdown: https://tttkmbb.com/conversion/temperature.md · JSON definition: https://tttkmbb.com/conversion/temperature.json
MCP: server https://tttkmbb.com/mcp, tool convert_temperature
OpenAPI operationId: convert_temperature
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Why is there no factor output?

Temperature scales have different zero points, so the conversion is affine (multiply and add), not a simple multiplication. The formula output shows the exact relation used.

Where do the scales coincide?

−40 °C = −40 °F. Absolute zero is 0 K = −273.15 °C = −459.67 °F = 0 °R; water freezes at 273.15 K and boils at 373.15 K at 1 atm.

Can I convert a temperature difference?

Not with this tool: a difference of Δ °C equals Δ × 9/5 °F and Δ K; entering it here would wrongly apply the 32 or 273.15 offset.

Related calculators

Specific Heat Calculator — Heat needed for a temperature change.
Ideal Gas Law Calculator — Gas calculations need absolute temperature in kelvin.