Celsius to Kelvin Converter

Kelvin starts at absolute zero, the lowest temperature there is, so a kelvin value is measured from a true zero. Celsius puts its zero at the freezing point of water, which is a convenient mark but not the bottom of the scale.

That matters whenever a formula multiplies or divides by temperature, as gas law and radiation formulas do. Heating air from 20 °C to 40 °C doesn't double its temperature in any physical sense. In kelvin it goes from 293.15 K to 313.15 K, an increase of about 6.8%. Put 20 and 40 into a gas law in Celsius and you'd predict twice the pressure, which is badly wrong.

The converter adds 273.15. Some textbooks and quick calculations use 273, which puts the answer 0.15 K low: 25 °C becomes 298 K instead of 298.15 K. Check which value your course or answer key uses, and stick to it through the whole problem.

The result can also carry more decimals than your measurement does. If a thermometer read 25.0 °C, one decimal place, report 298.2 K rather than 298.15 K. If the reading was a whole 25 °C, 298 K is the honest answer.

Keep the full 273.15 during the working and round only the final answer. Rounding each intermediate step can shift the last digit.

Celsius values can be negative; kelvin values can't. −40 °C is 233.15 K, and −273.15 °C is exactly 0 K. Nothing goes below that.

The converter enforces that floor. Type −300 °C and you get no result, only a note saying the value is below absolute zero. If you see that note, look for a typo or a stray minus sign in the input. Values right at the limit still work: −273.15 °C converts to 0 K.

Write the unit as K with no degree sign: 300 K, read as "300 kelvin".