Temperature Converter
F = C x 9/5 + 32. C = (F - 32) x 5/9. K = C + 273.15.
Choose the temperature scales
Enter the temperature value and choose the starting scale. Then choose Celsius, Fahrenheit or Kelvin as the output scale.
Use this for weather, cooking, science homework, travel and technical notes. Check the symbol carefully because C, F and K are not interchangeable.
For science formulas, confirm whether the problem asks for an absolute temperature or a temperature change. That choice can change whether Kelvin is required.
Reading warmer and colder scales
The converted value describes the same temperature on another scale. Celsius and Fahrenheit use different zero points and different degree sizes.
Kelvin uses the same degree size as Celsius, but its zero is absolute zero. That is why Celsius to Kelvin is an offset conversion.
Temperature conversion is not like length conversion because some formulas add or subtract a constant. You cannot always use simple multiplication.
Celsius, Fahrenheit, and Kelvin formulas
Celsius to Fahrenheit uses F = C x 9 / 5 + 32. Fahrenheit to Celsius uses C = (F - 32) x 5 / 9.
Celsius to Kelvin uses K = C + 273.15. Kelvin to Celsius uses C = K - 273.15.
For temperature differences, a change of 1 Celsius degree equals a change of 1 Kelvin. Fahrenheit differences use the 9/5 scale factor.
That difference between absolute temperature and temperature change is important in science problems. Read the wording before choosing the conversion.
Converting 68 F
To convert 20 C to Fahrenheit, calculate 20 x 9 / 5 + 32. That gives 68 F.
To convert 98.6 F to Celsius, subtract 32 to get 66.6, then multiply by 5 / 9. The result is 37 C.
To convert 25 C to Kelvin, add 273.15. The result is 298.15 K.
Kelvin cannot go below zero
The most common mistake is forgetting the plus 32 or minus 32 in Fahrenheit conversion. Celsius and Fahrenheit do not share the same zero.
Another mistake is using Celsius in formulas that require Kelvin. Gas law and thermodynamics formulas often need Kelvin because ratios must start from absolute zero.
Also avoid writing degrees Kelvin. The unit is written as kelvin or K, without a degree symbol in standard scientific style.
Temperature Converter FAQ
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 9 / 5, then add 32. For 20 C, 20 x 9 / 5 is 36, and 36 + 32 is 68 F.
For a rough mental estimate, double Celsius and add 30. That is not exact, but it is close for everyday weather.
Use the full formula when the number matters.
How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit value, then multiply by 5 / 9. For 68 F, subtract 32 to get 36. Then 36 x 5 / 9 gives 20 C.
The order matters. Subtract first, then multiply.
If you multiply first, the answer will be wrong because the Fahrenheit offset was not removed.
How do I convert Celsius to Kelvin?
Add 273.15 to the Celsius value. For 25 C, the result is 298.15 K.
Kelvin and Celsius have the same degree size. The difference is the zero point.
That is why a 10 C temperature change equals a 10 K change, even though 10 C is not 10 K as an absolute temperature.
Why do science formulas often use Kelvin?
Kelvin starts at absolute zero, so ratios and multiplication make physical sense in many formulas.
Celsius has an offset zero point based on water freezing. That is useful for everyday life, but not for every physics or chemistry equation.
If a formula includes temperature in a denominator or proportional relationship, Kelvin is often required.
Is negative Kelvin possible?
For ordinary temperature conversion, Kelvin values below 0 are not valid. Zero kelvin is absolute zero.
If a conversion from Celsius or Fahrenheit gives a negative Kelvin value, the input is below absolute zero and is not physically valid in normal use.
That usually means the entered value or scale was wrong.