Unlike length or weight, temperature scales don't share a common zero point, so conversions need addition or subtraction as well as multiplication. This converter handles the three most common scales: Celsius, Fahrenheit, and Kelvin.
The formulas
Celsius to Fahrenheit: F = C × 9/5 + 32
Fahrenheit to Celsius: C = (F − 32) × 5/9
Celsius to Kelvin: K = C + 273.15
Kelvin to Celsius: C = K − 273.15
Water boils at 100°C, which converts to 100 × 9/5 + 32 = 212°F, or 100 + 273.15 = 373.15 K.
Reference points
| Point | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Water freezes | 0 °C | 32 °F | 273.15 K |
| Water boils | 100 °C | 212 °F | 373.15 K |
| Absolute zero | −273.15 °C | −459.67 °F | 0 K |
Common mistakes
- Forgetting the offset. Unlike length or weight conversions, temperature scales (except Kelvin-to-Celsius) require adding or subtracting a constant, not just multiplying by a ratio.
- Treating Kelvin like Celsius with different labeling. Kelvin has no negative values in physical use — 0 K is absolute zero, the coldest physically possible temperature.
References
- National Institute of Standards and Technology (NIST) — official temperature scale definitions
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5, then add 32: F = C × 9/5 + 32.
What is absolute zero?
Absolute zero is 0 Kelvin, equal to −273.15°C or −459.67°F, the theoretical coldest possible temperature.
Why doesn't Kelvin use the degree symbol?
Kelvin is an absolute scale where each unit represents the same size step as Celsius but starts at absolute zero, so by international convention it's written as a plain number of kelvins, not “degrees Kelvin.”