Temperature is a scale we invented so “how hot” can be written as a number. Celsius, Fahrenheit, and Kelvin pick different zeros and different step sizes. Converting is not the same as converting metres to centimetres, because 0 °C is not 0 °F and neither is 0 K.
Everyday split: Celsius for most of the world and science labs (with Kelvin). Fahrenheit for US weather and many US ovens. Kelvin for physics when you need a scale that starts at absolute zero.
Celsius
Water freezes near 0 °C and boils near 100 °C at standard sea-level pressure. Room temperature is often quoted around 20–22 °C. Clinical body temperature is often discussed near 37 °C — actual readings vary by person, time of day, and thermometer site, so do not treat a blog number as a medical threshold.
Fahrenheit
Water freezes at 32 °F and boils at 212 °F at the same standard pressure. The degree is smaller: a 1 °C change is a 1.8 °F change. US forecasts and household ovens often use this scale. “It is 25 degrees” is incomplete; 25 °F is a freeze, 25 °C is a mild indoor day.
Kelvin
Kelvin uses the same step size as Celsius but starts at absolute zero. 0 K is the point where (classically) molecular motion is minimized. Ice water is about 273.15 K. You write 293 K, not 293 °K, in modern usage. You never use Kelvin for a baking recipe. The Temperature Converter rejects readings below absolute zero.
Temperature conversion formulas
| From → to | Formula |
|---|---|
| °C → °F | °F = °C × 9/5 + 32 |
| °F → °C | °C = (°F − 32) × 5/9 |
| °C → K | K = °C + 273.15 |
| K → °C | °C = K − 273.15 |
Example: to convert Celsius to Fahrenheit, 20 °C → 20 × 1.8 + 32 = 68 °F. The Fahrenheit to Celsius formula reverses that: subtract 32, then multiply by 5/9. Zero is a valid temperature (0 °C, 0 °F, 0 K); a converter should not treat 0 as “empty.” The Temperature Converter uses these identities and also supports Rankine (°R), an absolute scale with Fahrenheit-sized degrees.
When to pick which scale
- International recipes and lab notes: Celsius (Kelvin if the work is thermodynamic).
- Talking to someone who only knows US weather: give Fahrenheit or both.
- Never mix unlabeled “degrees” in a safety-critical procedure (vaccine storage, kiln, autoclave).
Easy mistakes
- Multiplying °C by 9/5 and forgetting to add 32.
- Converting 0 °C as if it were “no value.”
- Using Kelvin offsets on Fahrenheit by accident.
Convert a reading
Use the Temperature Converter when you do not want to restage the algebra by hand.
Open Temperature Converter →Cooking and ovens
Oven dials in the US are usually Fahrenheit. A recipe that says 180 °C is 356 °F, often rounded to 350 °F on household ovens. That rounding is a kitchen convention, not a claim that 180 °C equals 350 °F exactly. For lab or medical storage, do not round the conversion.
Weather “feels like” values mix humidity or wind; they are not a fourth temperature scale. Convert the actual reading, not the adjective.
Takeaway
Three scales, two that share a degree size (Celsius and Kelvin), one offset pair (Celsius/Fahrenheit). Label the unit every time; the math is short once the zero points are explicit.