Kelvin Converter

To convert Celsius to Kelvin, add 273.15 to the Celsius value. The formula is K = °C + 273.15. It works because zero on the Kelvin scale means absolute zero, not the freezing point of water.

Unlike Celsius to Fahrenheit, this conversion has no multiplication step. Room temperature at 20°C becomes 293.15 K, and the boiling point of water at 100°C becomes 373.15 K. The offset stays constant across the entire scale.

To convert Kelvin to Celsius, subtract 273.15 from the Kelvin value. The formula is °C = K − 273.15, which simply reverses the offset used going the other direction.

Kelvin values are always positive since the scale starts at absolute zero, so the result can still land below zero. A reading of 250 K converts to -23.15°C, which is well below freezing despite the Kelvin figure looking unremarkable.

To convert Kelvin to Fahrenheit, subtract 273.15 to get Celsius, then multiply by 9/5 and add 32. The formula is °F = (K − 273.15) × 9/5 + 32.

This is a two-step conversion in practice, since Fahrenheit and Kelvin do not share a direct offset the way Celsius and Kelvin do. Liquid nitrogen boils at 77 K, which works out to -320.47°F once both steps are applied.

To convert Fahrenheit to Kelvin, subtract 32, multiply by 5/9, then add 273.15. The formula is K = (°F − 32) × 5/9 + 273.15.

A typical room at 68°F converts to roughly 293.15 K, matching the earlier example at 20°C. Checking a result against its Celsius equivalent is a fast way to confirm your math.

Formulas are easier to trust once you see them applied to real reference points. The five examples below cover the values people actually look up, from everyday room temperature to physics-textbook extremes.

Each of these checks out against the formulas above, so you can use them to sanity-check your own calculations before trusting a result.

Developers who need Kelvin conversions in their own project can use the functions below instead of re-deriving the formulas. All four directions are covered, and the logic matches exactly what powers the calculator on this page.

function celsiusToKelvin(celsius) {
  return celsius + 273.15;
}

function kelvinToCelsius(kelvin) {
  return kelvin - 273.15;
}

function kelvinToFahrenheit(kelvin) {
  return (kelvin - 273.15) * 9 / 5 + 32;
}

function fahrenheitToKelvin(fahrenheit) {
  return (fahrenheit - 32) * 5 / 9 + 273.15;
}

Copy the block above directly into a JavaScript project. No dependencies are required, and the same four formulas apply regardless of language since they are pure arithmetic.

This Kelvin converter runs entirely in your browser using client-side JavaScript. The values you enter are never transmitted to our servers or stored anywhere outside your current session.

You can confirm this yourself by disconnecting your internet connection after the page loads. The tool keeps working normally, because no network request is involved in producing a result.

These are the most frequent errors people make with Kelvin conversions, along with the fix for each.

The table below lines up common reference points across all three scales for quick lookup.

Need Celsius and Fahrenheit specifically, without Kelvin? Our dedicated Celsius to Fahrenheit and Fahrenheit to Celsius converters cover that pair with their own worked examples and mental math shortcuts. For a single tool covering all three scales in every direction, see our full Temperature Converter.