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How to use
Celsius, Fahrenheit and kelvin use different origins and scale sizes. Fahrenheit conversion requires both a multiplication and an offset; absolute kelvin is Celsius plus 273.15. This converter passes through Celsius to calculate the target value and rejects inputs below absolute zero. It converts temperature readings, not temperature differences, which follow separate conversion rules.
- Enter a temperature and choose its source scale: °C, °F or K.
- Select the target scale; the tool converts via Celsius.
- Check against an easy benchmark: 25°C equals 77°F and 298.15 K.
- Values below −273.15°C (0 K) are rejected rather than displayed as valid temperatures.
How it is calculated
Example
Worked checks: 25°C × 9÷5 + 32 = 77°F; 25°C + 273.15 = 298.15 K. At −40°C the Fahrenheit reading is also −40°F. Absolute zero is 0 K, or −273.15°C, or −459.67°F. For a temperature difference, however, a change of 10°C equals a change of 18°F; do not add the 32° offset.
Important notes
Write kelvin as K, not °K. This calculator models ordinary absolute thermodynamic temperatures; a negative kelvin input is not valid here. To convert only a temperature interval, use a factor of 9/5 between Celsius and Fahrenheit without adding the 32-degree offset. Display rounding can slightly affect the last decimal digits.
Worked examples and interpreting results
Zero degrees Celsius equals 32°F and 273.15 K. Temperature conversion can require adding an offset, so a single multiplication factor does not work as it does for length conversion.
| Case | Calculation | Result |
|---|---|---|
| 0 Celsius to Fahrenheit | 0 × 9/5 + 32 | 32 °F |
| 0 Celsius to kelvin | 0 + 273.15 | 273.15 K |
| 68 Fahrenheit to Celsius | (68 − 32) × 5/9 | 20 °C |
How to check the result
A temperature difference differs from a temperature reading: a rise of 10°C equals a rise of 18°F without adding 32. Kelvin does not use a degree symbol; absolute readings below 0 K are outside this calculator’s ordinary domain.
Frequently asked questions
What is 25 Celsius in Fahrenheit and kelvin?
25 × 9/5 + 32 equals 77°F, while adding 273.15 gives 298.15 K. Both are readings of the same absolute temperature.
What temperature is absolute zero?
Absolute zero is 0 K, equivalent to −273.15°C or −459.67°F. This converter rejects values lower than that.
Is converting a 10°C temperature difference the same as converting 10°C?
No. A difference of 10°C equals a difference of 18°F; converting a reading of 10°C gives 50°F because the scale offset is included.