Celsius and Fahrenheit both measure temperature, but they use different zero points and different-sized degrees. Converting between them isn't a simple multiplication — you need to shift the scale as well.
To go from Celsius to Fahrenheit:
To go from Fahrenheit to Celsius:
The 9⁄5 (or 5⁄9 in reverse) accounts for the fact that a Fahrenheit degree is smaller than a Celsius degree — there are 180 degrees between freezing and boiling on the Fahrenheit scale, versus 100 on the Celsius scale. The +32 or −32 accounts for the fact that the two scales don't share a zero point: 0°C (freezing) is 32°F, not 0°F.
For a rough estimate without doing exact multiplication, double the Celsius value and add 30:
This isn't exact — the real multiplier is 1.8, not 2 — but it's close enough for everyday use like checking the weather. For anything that needs precision (cooking, science, medicine), use the exact formula or a converter.
| What | Celsius | Fahrenheit |
|---|---|---|
| Water freezes | 0°C | 32°F |
| Water boils (sea level) | 100°C | 212°F |
| Room temperature | ~20–22°C | ~68–72°F |
| Average human body temperature | 37°C | 98.6°F |
| A hot summer day | 32°C | 90°F |
| Freezer setting | −18°C | 0°F |
| Bread bakes | 180°C | 350°F |
| Pizza oven (hot) | 260°C | 500°F |
Celsius (originally centigrade) is defined so that 0°C is the freezing point of water and 100°C is the boiling point at standard atmospheric pressure, which makes it intuitive for science and most of the world's everyday use. Fahrenheit, developed earlier, uses a scale where 32°F and 212°F mark those same two points — an arrangement that made more sense with the mercury thermometers of its time.
Most countries adopted Celsius as part of a broader shift to the metric system. The United States is the most notable exception, still using Fahrenheit for weather, cooking, and everyday temperature references, even though Celsius is standard in its scientific and medical fields.
For exact conversions — including Kelvin — use the Temperature category on the UnitDial converter. It updates live as you type, so there's no formula to remember.