0 °C equals 273.15 K. 100 °C equals 373.15 K.
| Celsius (°C) | Kelvin (K) |
|---|---|
| -40 °C | 233.15 K |
| -20 °C | 253.15 K |
| -10 °C | 263.15 K |
| 0 °C | 273.15 K |
| 10 °C | 283.15 K |
| 20 °C | 293.15 K |
| 30 °C | 303.15 K |
| 37 °C | 310.15 K |
| 50 °C | 323.15 K |
| 100 °C | 373.15 K |
| 200 °C | 473.15 K |
| 500 °C | 773.15 K |
Temperature scales use fixed reference points rather than multiplicative factors, so converting between them requires a formula rather than simple multiplication. The Celsius and Kelvin scales differ in both their zero point and the size of their degrees.
For example: 0 °C = 273.15 K, and 100 °C = 373.15 K.
To convert in the reverse direction (Kelvin to Celsius): °C = K − 273.15
The Celsius scale (°C) was developed by Swedish astronomer Anders Celsius in 1742, though his original scale ran backwards from today's — he set 0 at the boiling point of water and 100 at freezing. The scale was inverted after his death to the familiar orientation, sometimes attributed to Carl Linnaeus. The Celsius scale anchors its two primary reference points to pure water: 0°C for the freezing point and 100°C for the boiling point at standard atmospheric pressure (101.325 kPa).
Celsius is the official temperature scale for everyday use in almost every country in the world, and the scientific community uses it alongside the Kelvin scale for all but the most fundamental thermodynamic calculations. Weather forecasts, medical thermometers, oven settings, refrigerator temperatures, and industrial process controls in metric countries all use Celsius. A comfortable room temperature is around 20–22°C; normal human body temperature is 37°C; and water, the most important liquid for life, boils at 100°C at sea level.
In the SI system, temperature differences and increments are the same in Celsius and Kelvin — a change of 1°C is identical to a change of 1 K. The Kelvin zero (absolute zero, −273.15°C) represents the lowest possible temperature, where molecular motion theoretically ceases entirely. The practical advantage of Celsius over Kelvin for everyday use is that the numbers are smaller and more intuitive for describing conditions on Earth's surface.
The Kelvin (K) is the SI base unit of thermodynamic temperature, named after William Thomson (Lord Kelvin), the Belfast-born physicist who first proposed an absolute temperature scale in 1848. Unlike Celsius or Fahrenheit, the Kelvin scale starts at absolute zero — the lowest theoretically possible temperature, defined as 0 K (equal to −273.15°C). There is no negative temperature on the Kelvin scale in the classical thermodynamic sense.
The Kelvin scale is essential in physics and chemistry because thermodynamic laws are expressed in terms of absolute temperature. The ideal gas law (PV = nRT), the Stefan-Boltzmann law for black-body radiation, and the Boltzmann factor in statistical mechanics all require temperature in Kelvin. A gas at 300 K has twice the thermal energy of the same gas at 150 K — a ratio that has no simple physical meaning in Celsius or Fahrenheit.
Since 2019, the Kelvin has been redefined in terms of the Boltzmann constant (k = 1.380649 × 10⁻²³ J/K), fixing the relationship between temperature and energy at the most fundamental level. The degree symbol is not used with Kelvin — you write 273.15 K, not 273.15°K. Temperatures of practical interest range from just above 0 K (ultracold experiments with Bose-Einstein condensates reach billionths of a kelvin) to millions of kelvin (stellar interiors and nuclear fusion reactors).
Use the formula: K = °C + 273.15. For example, 0 °C = 273.15 K and 100 °C = 373.15 K.
0 °C equals 273.15 K.
100 °C equals 373.15 K.