Temperature Converter: °C, °F, Kelvin & More

Every conversion on this page goes through Celsius as the hub: your value is first converted to degrees Celsius, then from Celsius to the target unit. These are the six formulas from Celsius to each other scale.

• Fahrenheit: °F = °C × 9/5 + 32
• Kelvin: K = °C + 273.15
• Rankine: °R = (°C + 273.15) × 9/5
• Réaumur: °Ré = °C × 4/5
• Delisle: °De = (100 − °C) × 3/2
• Newton: °N = °C × 33/100

To go the other way, each formula is simply inverted: °C = (°F − 32) × 5/9, °C = K − 273.15, °C = (°R − 491.67) × 5/9, °C = °Ré × 5/4, °C = 100 − °De × 2/3, and °C = °N × 100/33.

Sources: Celsius defined relative to the kelvin (t/°C = T/K − 273.15, exact) per the BIPM SI Brochure; Rankine, Réaumur, Delisle and Newton scales by their standard historical definitions; see also the NIST Guide for the Use of the International System of Units (SP 811).

Convert 25 °C to Fahrenheit. Multiply by 9/5 and add 32: 25 × 1.8 = 45, then 45 + 32 = 77 °F — a warm spring day.

The reverse trip works the same way. Convert 98.6 °F (normal body temperature) to Celsius: subtract 32 to get 66.6, multiply by 5/9, and you land on 37 °C. Converting 37 °C back gives 98.6 °F again, which is how you can sanity-check any temperature conversion: the round trip must return your starting value.

1. Enter the temperature. Type the number you want to convert, such as 100. Decimals and negative numbers are fine.
2. Pick the units. Choose the scale you are converting from and the one you are converting to — Celsius, Fahrenheit, Kelvin, Rankine, Réaumur, Delisle or Newton.
3. Press Calculate. You get the converted value plus the exact formula used, for example °F = 100 × 9/5 + 32 = 212 °F.

Unlike a length converter, where every value is physically possible, temperature has a hard floor: the calculator rejects anything below absolute zero (−273.15 °C) instead of returning a meaningless number. Converting a scale to itself simply returns your value unchanged.

Absolute zero — 0 kelvin, or −273.15 °C — is the lowest temperature that can exist. Temperature is a measure of how much atoms and molecules jiggle, and at absolute zero that motion reaches its quantum-mechanical minimum. You can get arbitrarily close in a lab (physicists have reached billionths of a degree above it), but the third law of thermodynamics says you can never quite get there, and you can never go below it.

This is why the calculator treats −273.15 °C as a hard boundary. A conversion that lands below it — say, −300 °C — is not a cold temperature waiting to be converted; it is a value that cannot exist in this universe, so the honest answer is an error, not a number. Note that Delisle is the odd one out on the diagram: it counts down from boiling, so larger Delisle numbers mean colder temperatures.

Seven scales survive because different jobs needed different tools. Celsius won everyday life almost everywhere, Fahrenheit held on in the United States, and the absolute scales — Kelvin and Rankine — rule science and engineering, where starting from zero makes the math cleaner.

The Réaumur, Delisle and Newton scales are museum pieces today, but they still show up in old texts, antique instruments and trivia — which is why a complete converter covers them. If you are converting measurements for a recipe or a shipment, you may also need our weight converter for kilograms, pounds and ounces.

Four landmarks anchor every scale: absolute zero, the freezing point of water, human body temperature and the boiling point of water. Memorize the Celsius column and the rest follow from the formulas.

Two rows are worth a second look. Delisle reads 0 at boiling and 150 at freezing — it runs backwards. And the Kelvin and Rankine columns hit exactly 0 at absolute zero, which is what makes them "absolute" scales: 200 K is genuinely twice as hot as 100 K, a statement that makes no sense in Celsius or Fahrenheit. Checking an unfamiliar row by hand is quick work with a scientific calculator and the formulas above.