Temperature Converter
Celsius, Fahrenheit, Kelvin and Rankine.
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Result
33.8 °F
1 celsius in fahrenheit
1 °C = 33.8 °F
Temperature Conversion Math Formula
Temperature is the one unit family where multiplying by a conversion factor is not enough. Length and weight scales all start from zero in the same place, so they only differ by a stretch. Celsius, Fahrenheit and Kelvin start from different zeros, so converting needs a shift as well as a stretch.
Mathematically each conversion is a straight line, y = mx + b. The slope m is the stretch between the degree sizes and b is the shift between the zero points. A Celsius degree and a kelvin are the same size, a Fahrenheit degree is 5/9 of a Celsius degree, and a Rankine degree is the same size as a Fahrenheit degree.
The formula
°F = °C × 9/5 + 32°C = (°F − 32) × 5/9K = °C + 273.15°R = °F + 459.67
Worked example 1: Body temperature: 37 °C in °F
37 × 9/5 = 66.666.6 + 32Answer: 98.6 °F
Stretch first (multiply by 9/5), then shift (add 32). Doing the shift first is the most common slip.
Worked example 2: A 72 °F room, in °C
72 − 32 = 4040 × 5/9Answer: 22.2222 °C
Now you undo the shift first (subtract 32) and then undo the stretch (multiply by 5/9). The order flips because you are running the first formula backwards.
Worked example 3: 300 K, in °F
300 − 273.15 = 26.85 °C26.85 × 9/5 + 32 = 48.33 + 32Answer: 80.33 °F
Kelvin has no degree sign. The converter moves every value through Celsius, so going from K to °F is two small formulas, one after the other.
Worked example 4: Absolute zero, 0 K, in °F
0 K − 273.15 = −273.15 °C−273.15 × 9/5 + 32 = −491.67 + 32Answer: -459.67 °F
The same point is 0 K, −273.15 °C, −459.67 °F and 0 °R. Nothing can be colder, which is why Kelvin and Rankine are called absolute scales and never go negative.
Common mistakes to avoid
- Treating a temperature difference like a temperature. If today is 10 °C warmer than yesterday, it is 18 °F warmer, not 50 °F. A difference only stretches, so you multiply by 9/5 and skip the +32. The +32 applies only when you convert a reading on the scale.
- Trusting "double it and add 30" too far. The shortcut is close in mild weather: 20 °C gives 70 °F against the true 68 °F. By 35 °C it gives 100 °F against the true 95 °F, and in the cold it drifts the other way: −10 °C gives 10 °F against the true 14 °F. Use the formula when the answer matters.
- Writing negative kelvin or "degrees Kelvin". The unit is the kelvin, written K, with no degree sign. A negative kelvin value cannot exist physically, so a result below 0 K means an input or a formula is wrong.
About temperature units
Celsius, Fahrenheit and Kelvin are all anchored to the behaviour of water or to absolute zero. Celsius puts freezing at 0 and boiling at 100, at standard atmospheric pressure. Fahrenheit puts the same two points at 32 and 212, a gap of 180 degrees instead of 100. Kelvin starts at absolute zero and uses the Celsius degree, so water freezes at 273.15 K.
Since 2019 the kelvin is defined by fixing the Boltzmann constant, and the Celsius scale follows from it: °C = K − 273.15. Rankine is the Fahrenheit-sized absolute scale. It appears mainly in US thermodynamics and engineering.
- Celsius (°C)0 at the freezing point of water and 100 at its boiling point, at one standard atmosphere. The standard in science and in most countries.
- Fahrenheit (°F)Water freezes at 32 °F and boils at 212 °F. Used for everyday temperatures in the US and a few other places.
- Kelvin (K)The SI unit. It starts at absolute zero, 0 K = −273.15 °C. A change of 1 K equals a change of 1 °C.
- Rankine (°R)An absolute scale with Fahrenheit-sized degrees: 0 °R = 0 K and 491.67 °R = 0 °C.
Temperature conversion table
| Value | °C | °F | K |
|---|---|---|---|
| Absolute zero | -273.15 | -459.67 | 0 |
| Where °C and °F meet | -40 | -40 | 233.15 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20 | 68 | 293.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Water boils (1 atm) | 100 | 212 | 373.15 |
Temperature converter FAQ
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (that is 1.8), then add 32. For 25 °C: 25 × 1.8 = 45, and 45 + 32 = 77 °F.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9. For 50 °F: 50 − 32 = 18, and 18 × 5/9 = 10 °C.
How do I convert Celsius to Kelvin?
Add 273.15. So 25 °C is 298.15 K and 0 °C is 273.15 K. To go back, subtract 273.15. Many textbooks round the constant to 273, which is fine for rough work.
At what temperature are Celsius and Fahrenheit the same?
At −40. Set C = 1.8C + 32, so −0.8C = 32 and C = −40. Both scales read −40 at that point.
What is absolute zero?
The lowest possible temperature, where particles have the least thermal motion that quantum mechanics allows. It is 0 K, −273.15 °C and −459.67 °F. Laboratories have cooled matter to a tiny fraction of a kelvin above it but never to exactly 0 K.
What are normal body and room temperatures in both scales?
A typical body temperature is 37 °C, which is 98.6 °F. A comfortable room is around 20 °C to 22 °C, or 68 °F to 71.6 °F.