Temperature Converter
Convert a temperature between Celsius, Fahrenheit, Kelvin and Rankine. The arithmetic is exact, so 98.6 °F gives exactly 37 °C and not 36.99999999999999, and the page shows the formula that was applied.
Result
Enter a temperature to convert.
The calculation runs in this browser tab. Nothing you enter is uploaded, saved or logged.
How do the temperature scales relate?
Celsius and Fahrenheit are relative scales with different zero points and different degree sizes, so converting is not just a multiplication. On the Celsius scale water freezes at 0 °C and boils at 100 °C at standard pressure; on Fahrenheit it freezes at 32 °F and boils at 212 °F, so a Celsius degree is 1.8 times as large as a Fahrenheit degree.
Kelvin and Rankine are absolute scales that start at absolute zero, the lowest possible temperature. A kelvin is the same size as a Celsius degree, and zero kelvin is −273.15 °C. A Rankine degree is the same size as a Fahrenheit degree, and 0 °R is −459.67 °F. Kelvin is the SI unit, written without a degree sign.
How to use the Temperature Converter
- Enter the temperature. Negative values are allowed, down to absolute zero.
- Choose the scale you are converting from and the scale you are converting to.
- Optionally choose how many decimals to round to; by default the exact value is shown, or 6 decimals when it does not end.
- Read the result and the formula used, then look at the table for the same temperature on all four scales.
Formula
- Celsius to Fahrenheit
- °F = °C × 9/5 + 32
- Fahrenheit to Celsius
- °C = (°F − 32) × 5/9
- Celsius to Kelvin
- K = °C + 273.15
- Fahrenheit to Rankine
- °R = °F + 459.67
Conversions between any two scales go through Celsius, using exact fractions: 9/5 and 5/9 are kept as fractions rather than as the rounded decimals 1.8 and 0.5555….
The two scales meet at −40: −40 °C is exactly −40 °F.
Worked example
Normal body temperature, 98.6 °F, in Celsius. Many tools show 36.99999999999999 because of floating-point error; here it is exact:
| Question | Result |
|---|---|
| Input: Temperature | 98.6 |
| Input: From | Fahrenheit (°F) |
| Input: To | Celsius (°C) |
| Input: Round to | Automatic |
| 98.6 °F equals | 37 °C |
| Formula | °C = (°F − 32) × 5/9 |
Assumptions and limits
- A temperature below absolute zero (−273.15 °C, −459.67 °F, 0 K) is impossible, and the converter refuses it with an explanation.
- Fractions that do not end, such as 100 °F = 37.777… °C, are rounded to 6 decimals and marked ≈, unless you choose a number of decimals yourself.
- The conversion is between temperature values. A temperature difference converts differently: a rise of 10 °C is a rise of 18 °F, with no 32 added.
- Rømer, Réaumur and other historical scales are not included.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (or 1.8) and add 32. For 20 °C: 20 × 1.8 = 36, plus 32 gives 68 °F. A mental shortcut is to double the Celsius value and add 30, which gives 70 °F here.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9. For 212 °F: 212 − 32 = 180, and 180 × 5/9 = 100 °C.
How do I convert Celsius to Kelvin?
Add 273.15. So 25 °C is 298.15 K, and absolute zero, −273.15 °C, is 0 K. Kelvin has no degree sign.
At what temperature are Celsius and Fahrenheit equal?
At −40. That is the only temperature at which the two scales give the same number.
What is absolute zero?
The lowest temperature that can exist: 0 K, −273.15 °C or −459.67 °F, where particles have minimal thermal motion. The converter does not accept anything colder.
How do I convert a temperature difference instead of a temperature?
Do not add or subtract 32 or 273.15. Only the size of the degree changes: multiply a Celsius difference by 1.8 to get a Fahrenheit difference, and divide by 1.8 for the reverse. A kelvin difference equals a Celsius difference.