Learn how the Celsius, Fahrenheit, and Kelvin temperature scales work, with the exact conversion formulas and worked examples.
Temperature is measured on three common scales (Celsius, Fahrenheit, and Kelvin), and converting between them comes down to a handful of simple formulas once you understand how each scale is defined.
Celsius is used for most everyday and scientific purposes internationally. Fahrenheit is used for everyday temperatures mainly in the United States. Kelvin is the scale used throughout science, particularly physics and chemistry, because it starts at absolute zero rather than an arbitrary reference point.
Celsius is the standard temperature scale across most of the world. Under standard atmospheric pressure (sea level), water freezes at 0°C and boils at 100°C, the two reference points the scale was originally built around.
Fahrenheit remains the everyday scale in the United States. Under the same standard conditions, water freezes at 32°F and boils at 212°F.
Kelvin is an absolute temperature scale used throughout science. 0 Kelvin represents absolute zero: the coldest temperature theoretically possible, where there is no negative Kelvin scale at all. Because Kelvin measures temperature from this true zero point rather than an arbitrary reference like the freezing point of water, it’s written simply as “K”, not “degrees Kelvin” or “°K”.
Example: Convert 20°C (room temperature) to Fahrenheit: (20 × 9/5) + 32 = 36 + 32 = 68°F.
Example: Convert 98.6°F (average body temperature) to Celsius: (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37.0°C.
Example: Convert 25°C to Kelvin: 25 + 273.15 = 298.15 K.
| Reference Point | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Freezing water (sea level) | 0°C | 32°F | 273.15 K |
| Room temperature (approx.) | ≈20°C | ≈68°F | ≈293 K |
| Average body temperature (approx.) | ≈37°C | ≈98.6°F | ≈310 K |
| Boiling water (sea level) | 100°C | 212°F | 373.15 K |
Room temperature and body temperature are approximate and can vary: by climate and preference for room temperature, and by individual and time of day for body temperature. Freezing and boiling points also shift at different altitudes and air pressures; the figures above assume standard sea-level pressure.
The Temperature Converter converts between Celsius, Fahrenheit, and Kelvin instantly, with no formulas to remember. Temperature is also one piece of the broader metric-versus-Imperial picture: see Metric vs Imperial: Understanding the Two Measurement Systems for how it fits alongside length and weight units.
Temperature Converter
Multiply the Celsius value by 9/5, then add 32. For example, 20°C becomes (20 × 9/5) + 32 = 68°F.
Subtract 32 from the Fahrenheit value, then multiply by 5/9. For example, 98.6°F becomes (98.6 − 32) × 5/9 = 37.0°C.
0°C is 32°F, the freezing point of water under standard atmospheric pressure.
Absolute zero is 0 Kelvin, equal to −273.15°C or −459.67°F. It’s the coldest temperature theoretically possible, representing the point where a system has the minimum possible thermal energy.
Because it starts at absolute zero rather than an arbitrary reference point like the freezing point of water, Kelvin makes calculations involving temperature and energy more straightforward, and it avoids negative numbers in most physical contexts.
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