Quick answer: Temperature converts between three scales: Celsius equals Fahrenheit minus 32 times 5 over 9, Fahrenheit equals Celsius times 9 over 5 plus 32, and Kelvin equals Celsius plus 273.15. Water freezes at 0 C or 32 F and boils at 100 C or 212 F. Kelvin is the scientific scale and never goes negative.
Last reviewed: September 2026
Key facts
- °F = °C × 9/5 + 32 and K = °C + 273.15.
- −40° is the same in °C and °F — the one point where the scales cross.
- Shows all three scales at once, so one conversion answers everything.
- Quick estimate: double the °C and add 30 ≈ °F.
Weather abroad, oven settings, science class — temperature scales refuse to agree. This free temperature converter translates between Celsius, Fahrenheit and Kelvin instantly, showing all three scales at once.
Enter a value and pick the from and to scales. Unlike other units, temperature needs an offset as well as a scale factor — which is why 0 °C is 32 °F, not 0 °F.
How to use
- Enter a temperature value.
- Choose the from and to scales.
- See the conversion plus all three scales below.
Temperature formulas
| Term | Meaning |
|---|---|
| °C | Celsius — water freezes at 0°, boils at 100°. |
| °F | Fahrenheit — water freezes at 32°, boils at 212°. |
| K | Kelvin — starts at absolute zero; same size degrees as Celsius. |
To go backwards: °C = (°F − 32) × 5/9. Kelvin can never be negative — 0 K is absolute zero.
Worked examples
Room temperature
25 °C → °F: 25 × 9/5 + 32 = 77 °F.
25 °C → K: 25 + 273.15 = 298.15 K.
Body temperature and the crossover
98.6 °F → °C: (98.6 − 32) × 5/9 = 37 °C — normal body temperature.
−40 → −40 × 9/5 + 32 = −40 °F. The scales meet at −40 — a handy sanity check.
Everyday temperatures on all three scales
| Event | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20 | 68 | 293.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |
| Oven (moderate) | 180 | 356 | 453.15 |
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (1.8) and add 32: 20 °C → 68 °F. For a quick estimate, double and add 30.
What is Kelvin used for?
Science. It starts at absolute zero (−273.15 °C), so 0 K means no thermal motion at all — and its degrees are the same size as Celsius degrees.
Why is −40 the same in °C and °F?
It is the single point where the two linear scales cross — a handy trivia fact and a good sanity check for converters.
Can Kelvin be negative?
No. 0 K is the coldest anything can be; negative Kelvin would mean colder than absolute zero, which is impossible.
Why does the US use Fahrenheit?
Historical momentum: Fahrenheit predates Celsius adoption, and the US never completed metrication. Most of the world uses Celsius.
Sources
Key takeaways
- °F = °C × 9/5 + 32; K = °C + 273.15.
- −40° is identical on both scales — the perfect quick check.
- For estimates: double the °C and add 30 ≈ °F.
Comments
Leave a comment