Celsius ⇄ Fahrenheit Converter

How to convert Celsius to Fahrenheit

To convert Celsius to Fahrenheit, use this formula:

°F = °C × 9/5 + 32

Example: 25 °C × 9/5 + 32 = 77 °F

How to convert Fahrenheit to Celsius

To convert Fahrenheit to Celsius, use this formula:

°C = (°F − 32) × 5/9

Example: (100 °F − 32) × 5/9 = 37.7778 °C

Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level, and the two scales show the same number at −40 degrees. Fahrenheit is used mainly in the United States; most other countries use Celsius.

Two scales with different zero points

Daniel Gabriel Fahrenheit published his scale in 1724, and Anders Celsius proposed his in 1742. Celsius’s original scale ran upside down, with 0 for boiling water and 100 for freezing; it was reversed a few years later. Today both scales are officially defined from the kelvin: absolute zero, 0 K, is −273.15 °C or −459.67 °F. Because the zero points differ, converting always needs both a multiplication and an offset, unlike most other unit pairs.

Oven temperatures

American recipes give oven settings in °F, usually in steps of 25, and converted recipes round them to a neat Celsius number. British recipes sometimes add a gas mark as well:

Recipes written for a conventional oven are often lowered by about 20 °C, or 25 °F in American recipes, for a fan (convection) oven; your oven’s manual is the best guide.

Body temperature and weather

Normal body temperature is usually given as about 37 °C (98.6 °F), although healthy readings vary from person to person, through the day and with where the temperature is taken. A reading of 38 °C (100.4 °F) or higher is generally considered a fever. In weather terms, 20 °C (68 °F) is mild, 30 °C (86 °F) is hot, and a home freezer at −18 °C is almost exactly 0 °F (−0.4 °F).

Quick mental math

• Celsius to Fahrenheit: double it and add 30. 20 °C → 70 °F (exact: 68 °F). The trick is exact at 10 °C and drifts by about 1 °F for every 5 °C away from it, so at 30 °C it gives 90 °F instead of 86 °F.
• Fahrenheit to Celsius: subtract 30 and halve. 80 °F → 25 °C (exact: 26.7 °C). Good enough for a weather forecast, not for baking or medicine.
• Mirror pairs. 16 °C ≈ 61 °F and 28 °C ≈ 82 °F: the digits swap, which makes two common weather temperatures easy to remember.

Common mistakes

• Converting a change in temperature like a reading. A rise of 10 °C is a rise of 18 °F, not 50 °F. For differences, multiply by 1.8 only; the 32 belongs to actual readings.
• Using the weather shortcut in the kitchen. “Double and add 30” turns 180 °C into 390 °F, but the true value is 356 °F, enough to burn a cake.
• Leaving out the unit. “It’s 30 degrees” is a hot day in Celsius and below freezing in Fahrenheit (−1.1 °C).

FAQ

Is 100 °F a fever?

100 °F is 37.8 °C, a little above the usual normal range but below the commonly used fever threshold of 100.4 °F (38 °C). For health decisions, follow the advice of a doctor or your local health service.

What is room temperature in Fahrenheit?

Room temperature is usually taken as about 20–22 °C, which is 68–72 °F.

What temperature should a fridge be?

Food-safety guidance commonly recommends 4 °C (40 °F) or colder for a refrigerator and −18 °C (0 °F) for a freezer.

How do I convert to kelvin?

Add 273.15 to the Celsius value: 20 °C is 293.15 K. A change of 1 K equals a change of 1 °C. The Unit Converter handles kelvin as well.

Need another unit? The Unit Converter converts length, weight, temperature, area, volume, speed, time, data, pressure and energy.