Celsius to Kelvin Converter

Celsius to kelvin: the quick answer and the formula

To convert celsius to kelvin, add 273.15 to the Celsius temperature. So 25 °C becomes 298.15 K, 0 °C becomes 273.15 K, and 100 °C becomes 373.15 K. There is no multiplication and no scaling factor, because both scales use the same size of degree. The only thing that changes is where each scale puts its zero point. This converter does that arithmetic for you instantly, in the browser, with no signup and no rounding surprises.

The reason the offset is exactly 273.15 is that the kelvin scale starts at absolute zero, the coldest temperature physically possible, while the Celsius scale starts at the freezing point of water. Water freezes at 273.15 K, which is defined as 0 °C. Once you know that single anchor, every conversion in either direction follows from it.

How to use this celsius to kelvin converter

The tool is built for speed. You do not need to remember the formula or open a calculator app.

1. Type your temperature into the Celsius field. Decimals and negative numbers both work, so −40 °C or 36.6 °C are fine.
2. Read the kelvin result immediately. The value updates as you type, with the +273.15 offset already applied.
3. Copy the answer, or change the input to compare several temperatures in a row.

If you need to go the other way, the reverse-direction kelvin to celsius converter subtracts 273.15 for you. Many people land here searching for a "kelvin converter to celsius" when they actually need the opposite calculation, so it is worth knowing both pages exist.

Celsius to kelvin formula and worked examples

The conversion is a single addition:

K = °C + 273.15

And the celsius to kelvin formula's mirror image, the kelvin to celsius formula, is just the same offset subtracted:

°C = K − 273.15

Because the gap between scales never changes, a one-degree rise in Celsius is always a one-kelvin rise. That makes mental math easy: take the Celsius number, add roughly 273, and you are within a fraction of a kelvin. The table below shows how to convert kelvin to celsius and back across the temperatures people search for most.

Working a single value by hand confirms the pattern. For 25 celsius to kelvin: 25 + 273.15 = 298.15 K. For 100 degree celsius to kelvin: 100 + 273.15 = 373.15 K. To reverse 273 kelvin to celsius: 273 − 273.15 = −0.15 °C, just below freezing. And 0 kelvin to celsius is −273.15 °C, the absolute coldest anything can get.

Common conversions and use cases

Kelvin shows up wherever temperature needs an absolute reference. Scientists use it because gas laws, thermodynamic equations, and color-temperature ratings only behave correctly when zero means zero energy, not the freezing point of water.

• Chemistry and physics homework. Ideal gas calculations (PV = nRT) require kelvin, so students constantly convert celsius to kelvin before plugging numbers in.
• Lab reporting. Standard temperature is often quoted as 25 °C, which is 298.15 K, the value behind "25 celsius to kelvin" searches.
• Lighting and photography. Bulb color is rated in kelvin; understanding the scale helps you read those ratings.
• Engineering. Thermodynamic cycles and efficiency formulas use absolute temperature throughout.

Here are a few more reference points people look up: 100 kelvin to celsius is −173.15 °C, 200 kelvin to celsius is −73.15 °C, 10 kelvin to celsius is −263.15 °C, and 1 kelvin to celsius is −272.15 °C. Notice every kelvin value below 273.15 maps to a sub-zero Celsius reading.

Why the kelvin scale exists

The kelvin scale was proposed by the physicist William Thomson, later Lord Kelvin, in the 1840s. He wanted a temperature scale with a true zero, a point where there is no thermal energy at all, rather than an arbitrary zero tied to water freezing. That point is absolute zero, and fixing it at 0 K is what makes kelvin an absolute scale.

This matters because many physical laws are proportional to temperature, and proportions only work from a real zero. Double the kelvin temperature of a gas at constant pressure and you double its volume; that relationship simply does not hold if you measure in Celsius, where zero is just the freezing point of water. The same logic underlies the ideal gas law, blackbody radiation, and the thermodynamic definition of temperature. Whenever a calculation involves a ratio of temperatures, kelvin is the scale that gives the right answer, which is why converting celsius to kelvin is a routine first step in physics and chemistry.

Kelvin is one of the seven base units of the International System of Units (SI), placing it alongside the meter, the kilogram, and the second. Since a 2019 redefinition, the kelvin is defined through a fixed value of the Boltzmann constant, a fundamental constant of nature, rather than through the properties of water. For everyday conversions none of that changes the arithmetic: you still just add or subtract 273.15.

Where you will meet kelvin in real life

Beyond the classroom, kelvin shows up in more places than most people expect. Light bulbs and camera settings use "color temperature" in kelvin: a warm, cozy bulb is around 2,700 K, neutral daylight is near 5,500 K, and a cool, bluish light is 6,500 K or higher. Astronomers describe the surface temperature of stars in kelvin, with the Sun sitting near 5,800 K. Weather and climate scientists often work in kelvin so that temperature differences and energy calculations stay consistent. Even cryogenics, the science of the very cold, is quoted in kelvin because the interesting action happens within a few kelvin of absolute zero. In all of these, knowing how to move between the everyday Celsius scale and kelvin keeps the numbers meaningful.

Common mistakes to avoid

Most errors come from treating kelvin like Fahrenheit, which it is not.

• Writing a degree symbol. Kelvin is never "degrees kelvin." Write 298.15 K, not 298.15 °K. The unit is just "kelvin."
• Multiplying instead of adding. There is no ×9/5 step here. That factor belongs to Fahrenheit conversions. Celsius and kelvin share the same degree size, so you only ever add or subtract 273.15.
• Rounding 273.15 to 273. For homework that is usually fine, but precise lab or exam work expects the full 273.15 offset. Dropping the 0.15 can cost marks.
• Forgetting negatives stay negative until 273.15. A reading like −50 °C is still a positive kelvin value (223.15 K) because absolute zero is far colder than anything on the everyday Celsius range.
• Going below zero kelvin. If a calculation hands you a negative kelvin number, something upstream is wrong, since 0 K is the absolute floor.

Tips and related converters

For everyday estimates, remember the three anchors: 0 °C = 273.15 K (freezing), 25 °C = 298.15 K (room), and 100 °C = 373.15 K (boiling). With those memorized you can sanity-check almost any result. When you need a different scale entirely, switch between Fahrenheit and Celsius with the celsius to fahrenheit converter or the fahrenheit to celsius converter, and jump straight from the imperial scale to absolute units with the fahrenheit to kelvin converter. You can find every temperature and measurement tool together on the unit converters hub.

Frequently asked questions

What is the celsius to kelvin formula? Add 273.15 to the Celsius temperature: K = °C + 273.15. There is no multiplication because both scales use the same size degree, so the conversion is a pure offset.

How do I convert kelvin to celsius? Subtract 273.15 from the kelvin value: °C = K − 273.15. For example, 300 K is 26.85 °C, and our kelvin to celsius converter does this instantly.

What is 25 celsius to kelvin? 25 °C equals 298.15 K, found by adding 273.15 to 25. This is the standard reference temperature used in many chemistry calculations.

What is 0 kelvin to celsius? 0 K is −273.15 °C, known as absolute zero. It is the coldest temperature possible, where molecular motion stops, and nothing can be colder.

What is 100 degree celsius to kelvin? 100 °C equals 373.15 K. This is the boiling point of water at standard atmospheric pressure, a useful upper anchor when estimating conversions.

Why does kelvin not use a degree symbol? Kelvin is an SI base unit, so its values are written as plain "K" (for example, 310.15 K) rather than "degrees kelvin." Only Celsius and Fahrenheit take the degree symbol.

Is the gap between Celsius and kelvin always 273.15? Yes. The offset never changes because both scales increase in equal-sized degrees. A rise of one Celsius degree is always a rise of exactly one kelvin.

What is 273 kelvin to celsius? 273 K is −0.15 °C, just below the freezing point of water. The exact freezing point is 273.15 K, which equals 0 °C.

Can kelvin be negative? No. Because the scale begins at absolute zero, kelvin values cannot go below 0 K. If a calculation produces a negative kelvin number, there is an error in the input.