Temperature Converter
Convert temperatures between Celsius, Fahrenheit and Kelvin.
Results update as you type.
About this calculator
A temperature converter changes a reading between Celsius, Fahrenheit, Kelvin and the older Rankine and Réaumur scales. Unlike most unit conversions these scales do not share a zero point, so the tool converts through Celsius using the exact offset-and-scale formulas rather than a single multiplier.
The core relationships are °F = °C × 9/5 + 32, K = °C + 273.15 and °R = (°C + 273.15) × 9/5. Because Fahrenheit both shifts the zero (by 32°) and stretches the degree size (by 9/5), you cannot convert it with a simple factor the way you can with length or weight.
Worked example: to convert 100 °C to Fahrenheit, 100 × 9/5 + 32 = 212 °F — the boiling point of water. To convert 98.6 °F to Celsius, subtract 32 then multiply by 5/9: (98.6 − 32) × 5/9 = 37 °C, normal body temperature. The "all units" table shows the same reading on every scale at once.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 and add 32. So 100 °C = 100 × 1.8 + 32 = 212 °F, the boiling point of water, and 0 °C = 32 °F, its freezing point.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9. For example 98.6 °F = (98.6 − 32) × 5/9 = 37 °C, normal human body temperature.
What is Kelvin?
Kelvin is the absolute temperature scale used in science. It uses the same degree size as Celsius but starts at absolute zero, so K = °C + 273.15. Water freezes at 273.15 K.
At what temperature are Celsius and Fahrenheit equal?
In this temperature converter the two scales read the same at −40°: −40 °C equals −40 °F. It is the single point where the +32 offset and the 9/5 scale factor cancel out.
What is normal body temperature in Celsius and Fahrenheit?
Normal human body temperature is about 37 °C, which equals 98.6 °F. A reading above roughly 38 °C (100.4 °F) is generally considered a fever.
What is absolute zero?
Absolute zero is the lowest possible temperature, 0 K, equal to −273.15 °C or −459.67 °F. At that point molecular motion is at its theoretical minimum.
What is the Rankine scale?
Rankine is an absolute scale like Kelvin but uses Fahrenheit-sized degrees, so it starts at absolute zero (0 °R) and water freezes at 491.67 °R. It appears in some engineering fields in the United States.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/temperature/curl
curl "https://calculator.free/api/v1/temperature/?amount=1&from=C&to=F"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/temperature/?" + new URLSearchParams({
"amount": "1",
"from": "C",
"to": "F"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.