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Temperature Converter
Enter a temperature, choose the scale it is on and the scale you want. The result appears with the same reading on the other two scales, plus a warning if the value is below absolute zero.
The conversion formulas
Temperature scales differ in both the size of the degree and the position of zero, so a plain multiplication is not enough. The calculator uses Celsius as a hub:
- Fahrenheit to Celsius:
°C = (°F − 32) × 5/9 - Celsius to Fahrenheit:
°F = °C × 9/5 + 32 - Celsius to Kelvin:
K = °C + 273.15 - Kelvin to Rankine:
°R = K × 9/5, which also equals°F + 459.67
A Celsius degree and a kelvin are the same size. A Fahrenheit degree and a Rankine degree are the same size, and each is 5/9 of a kelvin.
Anchor points to check against
| Reference | °C | °F | K | °R |
|---|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 | 0 |
| Water freezes (1 atm) | 0 | 32 | 273.15 | 491.67 |
| Normal body temperature, about | 37 | 98.6 | 310.15 | 558.27 |
| Water boils (1 atm) | 100 | 212 | 373.15 | 671.67 |
| Scales agree | −40 | −40 | 233.15 | 419.67 |
The boiling point of water falls as air pressure drops, so 100 °C applies at standard atmospheric pressure only.
Readings versus differences
The most frequent error is converting a temperature difference with the full formula. If a room warms by 10 °C, it warms by 18 °F, not by 50 °F. The 32 offset applies to a reading, never to a change. In the same way, a tolerance of ±2 °C is ±3.6 °F.
Another trap is the symbol: the kelvin is written K without a degree sign and is never called a "degree Kelvin". Since 2019 it is defined by fixing the Boltzmann constant, while the Celsius scale is defined as the kelvin scale shifted by 273.15.
Mental shortcuts and limits
For a rough Celsius to Fahrenheit estimate, double the figure and add 30. For 20 °C this gives 70 °F against an exact 68 °F, close enough for weather. Going back, subtract 30 and halve. The shortcut drifts at extremes, so use the calculator for cooking, lab work or anything with a safety margin.
This tool rejects values below absolute zero, because no physical system can reach them. If you see that message, the usual cause is a unit set to Fahrenheit when the number was Celsius.
Typical uses are reading oven dials and weather forecasts from another country, interpreting lab and engineering data given in kelvin, and checking thermometer specifications. Results are shown to about four decimals, with trailing zeros removed.
Worked example
A thermometer shows 37 degrees Celsius. What is that on the Fahrenheit scale?
Inputs
| Temperature | 37 |
|---|---|
| From | Celsius (°C) |
| To | Fahrenheit (°F) |
Result
37 °C = 98.6 °F
| Kelvin (K) | 310.15 |
|---|---|
| Rankine (°R) | 558.27 |
- These are readings on a scale, so the offset matters. For a temperature difference only the size of the degree matters: a change of 10 °C or 10 K is a change of 18 °F or 18 °R.
Accuracy note: Factors use the standard definitions stated on this page. Results are rounded for display; for engineering or legal work use the full-precision factors.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (1.8) and add 32. For example, 100 °C × 1.8 + 32 = 212 °F.
At what temperature are Celsius and Fahrenheit equal?
They are equal at −40. Substituting into either formula gives the same number on both scales.
What is 0 kelvin in Celsius?
0 K is absolute zero, which is −273.15 °C or −459.67 °F.
What is the Rankine scale used for?
Rankine is an absolute scale that uses Fahrenheit-sized degrees, with 0 °R at absolute zero. It appears mainly in some US engineering and thermodynamics work.
Why does the converter refuse some values?
Anything below absolute zero is physically impossible, so the tool returns an error instead of a meaningless number.
Related calculators
More conversion references
For temperature conversion tables beyond this tool, see PakMath temperature conversion tables. PakMath is a sister project of Adzita.