Celsius to Kelvin converter

• K = °C + 273.15
• °C = K − 273.15
• K = (°F − 32) × 5/9 + 273.15

Example: room temperature, 20 °C, is 20 + 273.15 = 293.15 K. A kelvin is the same size as a Celsius degree, so only the zero point moves; nothing is multiplied.

To go from kelvin to Fahrenheit, convert to Celsius first and then use °F = °C × 9/5 + 32, or use K × 9/5 − 459.67 directly. In physics and chemistry problems, keep the full 273.15 unless your teacher or textbook says to round to 273. Temperature differences are the same in both scales: a rise of 10 °C is a rise of 10 K, which is why lab results often quote changes in K even when the starting point was measured in °C.

Absolute zero, 0 K, is the lowest temperature possible: the point at which a system has the minimum possible thermal energy. Nothing can be colder, so the Kelvin scale has no negative numbers. If you get a negative kelvin value, check that you subtracted instead of added. Scientists use kelvin because many physical laws, such as the ideal gas law (PV = nRT), only work with an absolute temperature.

Kelvin is written without a degree sign: 300 K, not 300 °K. The unit name is lowercase ("300 kelvins" or "300 kelvin"), while the symbol is a capital K. Since 2019 the kelvin has been defined in the SI by fixing the value of the Boltzmann constant, but for everyday conversions the 273.15 offset is all you need.

The Rankine scale is the Fahrenheit-sized version of kelvin: it also starts at absolute zero, but each degree is a Fahrenheit degree (0 °R = −459.67 °F). It still appears in some US engineering work, but kelvin is the standard in science.

You'll see kelvin on light bulb boxes as color temperature. Warm white bulbs are around 2700 K to 3000 K, neutral white around 4000 K and daylight bulbs around 5000 K to 6500 K. These numbers describe the color of the light, not how hot the bulb gets. For everyday weather and cooking conversions, the Celsius to Fahrenheit converter has charts for °C and °F. Everything is calculated in your browser.