How to use the temperature converter
- Type your number into Temperature. Negatives and decimals such as -40 or 98.6 work.
- Choose what that number is measured in under Unit: Fahrenheit (°F), Celsius (°C) or Kelvin (K).
- Read the three cards under Converted temperatures. Each shows the converted value and the formula that produced it.
- Change Decimals (0 to 4) for fewer or more digits. The default is 2 and trailing zeros are dropped, so 37 shows as 37, not 37.00.
Temperature conversion formulas
Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea-level pressure. That is 100 Celsius degrees against 180 Fahrenheit degrees, so one Celsius degree equals 1.8 Fahrenheit degrees. Kelvin uses the same step as Celsius and starts at absolute zero, which is -273.15 °C. These are the formulas the converter applies, and they match the conversion table in the NIST Guide to the SI:
- °F to °C:
(°F - 32) × 5/9 - °C to °F:
°C × 9/5 + 32 - °C to K:
°C + 273.15 - K to °C:
K - 273.15 - °F to K:
(°F + 459.67) × 5/9 - K to °F:
K × 9/5 - 459.67
Worked example: 72 °F
The page opens with 72 entered in Fahrenheit, so you see an answer straight away: 22.22 °C and 295.37 K. By hand, Celsius is (72 - 32) × 5/9 = 40 × 5/9 = 22.2222..., shown as 22.22. Kelvin is (72 + 459.67) × 5/9 = 295.3722..., shown as 295.37.
Limits and edge cases
- Anything below absolute zero (0 K, -273.15 °C, -459.67 °F) gets a warning instead of a result, because no object can be colder.
- Only the display is rounded. The math keeps full precision, so converting 22.22 °C back gives 71.996 °F, not exactly 72.
- Values of 1e15 and above are shown in scientific notation.
- This converts a temperature reading, not a temperature change. A rise of 10 °C is a rise of 18 °F: multiply by 1.8 and do not add 32.
- Water boils at 100 °C only at standard sea-level pressure. It boils at a lower temperature at altitude.
- Rankine and Réaumur are not included. For other units, use the Unit Converter.
Frequently asked questions
How do you convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9. For example, 98.6 °F minus 32 is 66.6, and 66.6 × 5/9 = 37 °C.
At what temperature are Fahrenheit and Celsius the same?
At -40. Setting (F - 32) × 5/9 equal to F and solving gives F = -40, so -40 °F is exactly -40 °C.
Can Kelvin be negative?
No. Kelvin starts at absolute zero (0 K, or -273.15 °C), the lowest temperature an ordinary object can have, so this converter shows a warning for anything below it instead of a result.
What is 350 degrees Fahrenheit in Celsius?
350 °F is 176.67 °C, or 449.82 K. Recipes round it to 175 °C or 180 °C. For gas marks and fan oven adjustments, use the Oven Temperature Converter.
Is there a quick way to estimate Celsius to Fahrenheit in my head?
Double the Celsius value and add 30. For 20 °C that gives 70 °F against the exact 68 °F. The estimate drifts further off in very hot or very cold weather, so use the converter when the number matters.
Sources: NIST Guide to the SI, Appendix B.8 (Fahrenheit, Celsius and kelvin conversion formulas) and NIST: the kelvin (absolute zero).