Temperature Converter
Convert Celsius, Fahrenheit and Kelvin (with the offset that a plain multiplication misses).
1 °C = 33.8 °F
Quick conversions
This converts between Celsius, Fahrenheit and Kelvin.
Temperature is the one conversion needing an offset as well as a multiplier, which is why the arithmetic is unlike other units.
How temperature scales convert
Temperature is unusual among unit conversions because the scales have different zero points as well as different step sizes. Converting metres to feet is one multiplication; converting Celsius to Fahrenheit needs a multiplication and an offset.
F = C × 9/5 + 32. The 9/5 handles the different degree size, since a Celsius degree is 1.8 times a Fahrenheit one. The +32 handles the different zero: water freezes at 0 °C and 32 °F.
There is exactly one temperature where the two scales agree: −40 °C is −40 °F. It is the single crossing point of two lines with different slopes, and a useful sanity check on any conversion.
Both scales are linear, so they cross exactly once. Everything else follows from the slope of 9/5 and the offset of 32.
What to enter
- Temperature value
- The number to convert.
- From and to scales
- Celsius, Fahrenheit or Kelvin. Kelvin has no degree symbol and no negative values.
The three scales
- Celsius
- 0 at water's freezing point, 100 at boiling. Used by most of the world.
- Fahrenheit
- 32 freezing, 212 boiling. Used in the US, and a smaller degree gives finer resolution without decimals.
- Kelvin
- Starts at absolute zero. K = C + 273.15. Used in science, and it has no negative values.
- Absolute zero
- 0 K, −273.15 °C, −459.67 °F. The point at which molecular motion is minimal.
- Body temperature
- About 37 °C, which is 98.6 °F.
What this assumes
Kelvin uses no degree symbol: 300 K, not 300 °K. It is a convention, and a common error in written work.
For temperature differences rather than absolute values, no offset applies: a change of 10 °C is a change of 18 °F.
How to calculate temperature conversion
Multiply for the degree size, then add or subtract for the zero point.
- 9/5 = 1.8
- A Celsius degree is 1.8 times a Fahrenheit degree
- 32
- The offset between the two zero points
Celsius to Fahrenheit: multiply first. 20 × 1.8 = 36, then add 32 to get 68 °F. Order matters.
Fahrenheit to Celsius: subtract first. (68 − 32) = 36, then × 5/9 = 20 °C. Subtracting after multiplying gives the wrong answer.
For Kelvin, just add 273.15. Kelvin shares Celsius's degree size, so there is no multiplication involved.
Sanity-check against a known point. 0 °C is 32 °F, 100 °C is 212 °F, and −40 is −40. If your answer breaks one of these, the order of operations is wrong.
See a worked example: converting in both directions
- Value
- 20 °C
To Fahrenheit: (20 × 9/5) + 32 = 36 + 32 = 68 °F.
Back again: (68 − 32) × 5/9 = 36 × 5/9 = 20 °C.
To Kelvin: 20 + 273.15 = 293.15 K.
A quick mental estimate: double the Celsius and add 30. That gives 70 for 20 °C, close enough for weather.
20 °C = 68 °F = 293.15 K
Frequently asked questions
Multiply by 9/5, then add 32. So 20 °C is (20 × 1.8) + 32 = 68 °F.
The order matters. Adding 32 first and then multiplying gives a completely different and wrong answer.
Double it and add 30. 20 °C gives 70 °F against a true 68; 30 °C gives 90 against a true 86.
It is close enough for weather and drifts at higher temperatures, since it uses 2 instead of 1.8. For cooking or anything precise, use the real formula.
−40 degrees. −40 °C is exactly −40 °F, and it is the only temperature where the two scales agree.
It follows from the algebra: the two lines have different slopes, so they cross exactly once.
Scientific work, because it starts at absolute zero and has no negative values, which makes it the right scale for physics equations.
Its degrees are the same size as Celsius, so K = C + 273.15. Note it is written without a degree symbol: 300 K, not 300 °K.
Historical inertia, mostly. Fahrenheit came first in English-speaking countries, and the US never completed metrication after the 1975 Metric Conversion Act made it voluntary.
It does have one practical advantage for weather: the smaller degree gives finer resolution, so everyday temperatures span a wider range of whole numbers.
No offset. For differences, only the scale factor applies: a change of 10 °C is a change of 18 °F.
Applying the +32 to a difference is a common error. The offset only applies to absolute temperatures, not to changes in them.
Problems people actually run into
Getting the order of operations wrong
Adding 32 before multiplying, or multiplying before subtracting when going the other way, produces answers that are badly wrong rather than slightly off.
Celsius to Fahrenheit: multiply, then add. Fahrenheit to Celsius: subtract, then multiply. Check against 0 °C = 32 °F to confirm.
Applying the offset to a difference
"The temperature rose 10 °C" converts to a rise of 18 °F, not 50 °F. Differences use only the 9/5 factor.
The +32 exists to reconcile two different zero points, and a change in temperature has no zero point to reconcile.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Last updated: September 4, 2026