Temperature Converter

Convert a temperature between Celsius, Fahrenheit, Kelvin, Réaumur, and Rankine, with all five values shown at once alongside key reference points like freezing, boiling, and body temperature.

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Temperature

Convert temperature between Celsius, Fahrenheit, Kelvin, and more

Enter a temperature value and choose a unit — all five scales are shown at once: Celsius, Fahrenheit, Kelvin, Réaumur, and Rankine.

Celsius

20°C

Fahrenheit

68°F

Kelvin

293.15K

Réaumur

16°Ré

Rankine

527.67°Ra

Reference points

Water freezes 0°C  /  32°F  /  273.15 K
Water boils 100°C  /  212°F  /  373.15 K
Normal body temp 37°C  /  98.6°F  /  310.15 K
Room temperature 22°C  /  71.6°F  /  295.15 K
Absolute zero -273.15°C  /  -459.67°F  /  0 K

Temperature

Temperature conversion: Celsius, Fahrenheit, Kelvin, and the other scales explained

A temperature converter translates any temperature reading into all common scales at once. This tool covers Celsius, Fahrenheit, Kelvin, Réaumur, and Rankine — so whether you are reading a weather forecast, a scientific dataset, a recipe, or an engineering spec, you get every equivalent in one place.

Why five temperature scales exist

Temperature scales were developed independently by different scientists before the metric system was standardised. Gabriel Fahrenheit introduced his scale in 1724; Anders Celsius published his in 1742; William Thomson (Lord Kelvin) proposed the absolute thermodynamic scale in 1848. René-Antoine Ferchault de Réaumur created an earlier scale in 1730, now rarely used outside wine-making and some Eastern European food traditions. Rankine is the absolute counterpart to Fahrenheit, used mainly in some US engineering fields.

Today, Celsius is the global everyday standard; Fahrenheit persists in the US and a few other countries for weather and cooking; Kelvin is the SI base unit for thermodynamic temperature used in science and engineering. Réaumur and Rankine appear in specialist or historical contexts.

How each conversion works

All conversions flow through Celsius as the intermediate. Fahrenheit: °C = (°F − 32) × 5/9; reverse: °F = °C × 9/5 + 32. Kelvin: K = °C + 273.15; reverse: °C = K − 273.15. The key fact about Kelvin is that 0 K is absolute zero — the theoretical minimum temperature where all molecular motion stops. There are no negative Kelvin values.

Réaumur: °C = °Ré × 5/4; reverse: °Ré = °C × 4/5. Rankine: °Ra = (°C + 273.15) × 9/5; reverse: °C = (°Ra − 491.67) × 5/9. Rankine has the same zero point as Kelvin (absolute zero) but uses Fahrenheit-sized degrees, so 0°Ra = 0 K and 491.67°Ra = 0°C.

Key fixed reference points

Water freezes at 0°C / 32°F / 273.15 K. Water boils at 100°C / 212°F / 373.15 K (at sea-level atmospheric pressure). Normal human body temperature is 37°C / 98.6°F / 310.15 K. Room temperature is typically around 20–22°C / 68–72°F / 293–295 K. Absolute zero is −273.15°C / −459.67°F / 0 K.

A useful mental trick for everyday Celsius/Fahrenheit conversion: double the Celsius value and add 30 to get a rough Fahrenheit estimate (e.g. 20°C → 70°F, actual 68°F). For exact values, always use the formula or this converter.

Practical uses: weather, cooking, and science

Weather: US forecasts use °F; most of the world uses °C. A temperature of 100°F (37.8°C) is a very hot summer day; 0°C (32°F) is the freezing point. For travel and international weather, this converter lets you quickly contextualise forecasts.

Cooking: recipes from the UK and Australia use °C; US recipes use °F. Oven conversions like 180°C to °F (356°F) are a common kitchen need. Science: thermodynamic calculations, gas laws, and cryogenics require Kelvin. Any formula that multiplies or divides by temperature must use Kelvin to avoid division-by-zero or sign errors.

Frequently asked questions

What is the formula to convert Celsius to Fahrenheit?

°F = (°C × 9/5) + 32. For example, 20°C = (20 × 1.8) + 32 = 36 + 32 = 68°F. The reverse is °C = (°F − 32) × 5/9.

 At what temperature are Celsius and Fahrenheit the same?

−40° is the point where both scales read the same value. At −40, the Celsius and Fahrenheit scales intersect: −40°C = −40°F. You can verify with the formula: (−40 × 9/5) + 32 = −72 + 32 = −40.

 Can Kelvin be negative?

No. Kelvin is an absolute scale with 0 K defined as absolute zero — the lowest possible temperature. All physically meaningful temperatures are 0 K or above. Negative Kelvin values have no physical meaning in classical thermodynamics (some quantum-mechanical systems are described using negative effective temperatures, but this is a different use of the term).

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