Celsius to Kelvin
Convert celsius to kelvin instantly — type a value and read the result, with the exact formula shown.
Example
0 °C = 273.15 K, 25 °C = 298.15 K, 100 °C = 373.15 K.
How it works
K = °C + 273.15. Every value is converted through a single kelvin base unit using internationally defined conversion factors, so any from/to pair stays consistent.
Good to know
Converting Celsius to Kelvin shows up constantly in chemistry, physics, and engineering work, because the gas laws (PV = nRT), thermodynamic equations, and most scientific software demand temperatures on an absolute scale. A reading of 25 °C in a lab notebook becomes 298.15 K the moment you plug it into a calculation, and skipping that step is one of the most common sources of wrong answers in homework and process design.
Both units are metric, but they answer different questions. Celsius (introduced by Anders Celsius in 1742) is a relative scale pinned to water: 0 °C at freezing and 100 °C at boiling under standard pressure. Kelvin, named for William Thomson, Lord Kelvin, is an absolute scale that starts at 0 K — absolute zero, the point where molecular motion is at its theoretical minimum. Crucially, the two scales share the same degree size, so a change of 1 °C equals a change of exactly 1 K. That is why the conversion is a simple offset, not a stretch-and-shift like Fahrenheit.
The rule of thumb is the easiest in all of temperature work: add 273.15 to go from Celsius to Kelvin, and subtract it to come back. If you only need a ballpark, rounding to 273 is usually close enough for mental math — 20 °C is roughly 293 K. Note that Kelvin is written without a degree symbol (it is "300 K", never "300 °K").
The most common mistake is treating temperature differences the same as temperatures. When you convert a single reading, you add the 273.15 offset; but when you convert a temperature interval or a rate (say, a 10-degree rise), you do not add anything — a 10 °C difference is a 10 K difference. The other trap is precision: the offset is 273.15, not 273, and dropping the .15 quietly skews results in sensitive calculations.
Frequently asked questions
How do you convert celsius to kelvin?
Use K = °C + 273.15. This tool applies that formula automatically as you type.
What is a quick reference for Celsius to Kelvin?
0 °C = 273.15 K; 25 °C = 298.15 K; 100 °C = 373.15 K.
Is this converter free and private?
Yes. It runs entirely in your browser, so your inputs never leave your device, there is no sign-up, and it works offline once loaded.
Are the conversions exact?
Conversions use internationally defined factors and are exact where the definitions are exact (for example, 1 inch = 2.54 cm). Displayed results are rounded for readability.
People also ask
Why do you add 273.15 to convert Celsius to Kelvin?
Because 0 K (absolute zero) sits 273.15 degrees below 0 °C (the freezing point of water). Since both scales use the same degree size, you simply shift the zero point by adding 273.15.
What is 37 °C in Kelvin?
37 °C equals 310.15 K (37 + 273.15). That is normal human body temperature on the absolute scale.
Can a Kelvin temperature ever be negative?
No. Kelvin starts at absolute zero (0 K), which is the lowest physically possible temperature, so all real temperatures are positive on this scale. Only Celsius and Fahrenheit can show negative values.
What is room temperature in Kelvin?
Room temperature of about 20–22 °C is roughly 293.15 to 295.15 K. Scientists often use 298.15 K (25 °C) as a standard reference temperature.
Is a change of 1 °C the same as a change of 1 K?
Yes. The two scales have identical degree increments, so any temperature interval or difference is numerically the same in Celsius and Kelvin — only single readings need the 273.15 offset.
Why does Kelvin not use a degree symbol?
By international convention (SI), Kelvin is treated as a base unit, not a degree-based scale, so you write '300 K' rather than '300 °K'. The word 'degrees' is also dropped.
What is absolute zero in Celsius?
Absolute zero is 0 K, which equals −273.15 °C. It is the theoretical point at which molecular motion reaches its minimum and cannot be physically reached.
Why do scientists prefer Kelvin over Celsius?
Because gas laws and thermodynamic equations require an absolute scale where temperature is directly proportional to energy. Using Celsius in those formulas would give nonsensical results, such as dividing by zero or negative temperatures.
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