The temperature converter converts between Celsius, Fahrenheit, and Kelvin using exact linear formulas. It handles negative values and rejects temperatures below absolute zero in the selected source scale.
How to use this calculator
Enter the temperature and select source and target scales. Celsius and Kelvin have the same interval size but different zero points. Fahrenheit uses a different interval size and offset.
Formula & calculation method
C = K − 273.15; C = (F − 32) × 5/9; F = C × 9/5 + 32; K = C + 273.15The calculator first converts the input to Celsius and then to the target scale. Absolute zero is −273.15°C, −459.67°F, or 0 K, and lower physical temperatures are not accepted.
Worked example
25°C converts to 77°F and 298.15 K. A temperature of −40 is the same numeric value on Celsius and Fahrenheit scales, which provides a useful formula check.
Why this is useful
Exact formulas preserve both differences and offsets, unlike simple multiplication. Validation for absolute zero prevents physically invalid output while still allowing ordinary negative temperatures.
Limitations to keep in mind
The converter changes temperature units only; it does not calculate heat, thermal energy, wind chill, or perceived temperature. Display rounding can be adjusted only through the output formatting, not the physical formulas.
Frequently asked questions
Why is −40 special?
Because the Celsius and Fahrenheit scales intersect at −40, so −40°C equals −40°F.
Can Kelvin be negative?
No. Zero Kelvin is absolute zero, so the calculator rejects negative Kelvin and equivalent values below absolute zero.
Is a degree Celsius the same size as one Kelvin?
Yes for temperature differences. Their zero points differ by 273.15, but their interval sizes are identical.