What this temperature converter does
This tool converts temperature between the three scales in everyday and scientific use: Celsius, used by most of the world for weather, cooking and daily life; Fahrenheit, still standard in the United States; and Kelvin, the scientific scale used in physics and chemistry. Unlike length or weight, temperature scales do not share a zero point, so converting them takes a formula rather than a simple multiplication — which is exactly why a converter is worth using instead of guessing. Type any value, including negatives, and you will see it in your chosen scale and in all three scales in the table below the result.
The situations are endless and familiar: a weather forecast on holiday ("28 degrees — is that warm?"), an American recipe that says bake at 350 degrees read by a cook whose oven is marked in Celsius, a child's temperature taken on a thermometer in one scale and reported to a doctor who thinks in the other, or a science lesson that introduces Kelvin and absolute zero. Body temperature is the conversion people make under stress, so it is worth knowing the landmarks by heart: 37°C (98.6°F) is the traditional "normal", and 38°C (100.4°F) is the commonly used fever threshold.
How to use it
- Type the temperature into the From box.
- Pick the scale it is in, then the scale you want.
- Read the answer. Press Swap to reverse direction, and check the table for all three scales at once.
The formulas
| Conversion | Formula | Example |
|---|---|---|
| Celsius → Fahrenheit | °F = °C × 9/5 + 32 | 100°C → 212°F |
| Fahrenheit → Celsius | °C = (°F − 32) × 5/9 | 32°F → 0°C |
| Celsius → Kelvin | K = °C + 273.15 | 0°C → 273.15 K |
| Kelvin → Celsius | °C = K − 273.15 | 273.15 K → 0°C |
The "+ 32" is the part everyone forgets, and it exists because the scales start in different places: Celsius sets zero at the freezing point of water, while Fahrenheit sets zero at the coldest temperature its inventor could make in his laboratory with a salt-and-ice mixture. The degrees are also different sizes — a Fahrenheit degree is only 5/9 as large as a Celsius degree — which is why the formula both multiplies and adds. Kelvin is the simplest of the three: it uses the same size degree as Celsius and simply shifts the zero down to absolute zero, the point at which matter has the least possible heat energy. That is why Kelvin values are never negative, and why scientists prefer the scale.
Reference temperatures worth knowing
| What | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | −273.15°C | −459.67°F | 0 K |
| Water freezes | 0°C | 32°F | 273.15 K |
| Scales meet | −40°C | −40°F | 233.15 K |
| Room temperature | 21°C | 69.8°F | 294.15 K |
| Normal body temperature | 37°C | 98.6°F | 310.15 K |
| Fever threshold | 38°C | 100.4°F | 311.15 K |
| Water boils (sea level) | 100°C | 212°F | 373.15 K |
| Typical home oven | 180°C | 356°F | 453.15 K |
A quick mental shortcut
For rough weather conversions you do not need the exact formula. To estimate Fahrenheit from Celsius, double the Celsius figure and add 30: 20°C → 70°F estimated, 68°F exact — close enough to decide on a jacket. To estimate Celsius from Fahrenheit, subtract 30 and halve: 80°F → about 25°C, versus 26.7°C exact. For oven temperatures and anything medical, skip the shortcut and use the converter above.
Frequently asked questions
What is the formula to convert Celsius to Fahrenheit?
°F = °C × 9/5 + 32. So 20°C × 1.8 + 32 = 68°F. Going back: subtract 32, then multiply by 5/9.
Where are Celsius and Fahrenheit equal?
At −40: forty below zero is the same temperature on both scales.
What is normal body temperature?
Traditionally 37°C / 98.6°F, though healthy people vary roughly between 36.1°C and 37.2°C (97–99°F) through the day. This converter is for general reference, not medical advice.
Why does Kelvin have no degree symbol?
By convention, kelvin is written without the degree sign — 300 K, not 300 °K — because it is an absolute scale with a true zero, like meters or kilograms.
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