Celsius to Kelvin
°C
K
Conversion History
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Quick Reference Table (Celsius to Kelvin)
| Celsius (°C) | Kelvin (K) |
|---|---|
| -40 | 233.15 |
| 0 | 273.15 |
| 20 | 293.15 |
| 37 | 310.15 |
| 100 | 373.15 |
About Celsius (°C)
Celsius (°C) is the most widely used temperature scale in the world, adopted by every country except the United States, Liberia, and Myanmar for everyday and scientific use. Zero degrees Celsius is defined as the freezing point of water at standard atmospheric pressure; 100°C is the boiling point. Originally called centigrade because of its 100-degree span between these two reference points, it was renamed Celsius in 1948 to honor Swedish astronomer Anders Celsius. It is the practical temperature scale for weather, cooking, medicine, and most scientific work outside thermodynamics. Body temperature is 37°C; a comfortable room is typically 20–22°C.
Water freezes at 0°C and boils at 100°C. Normal human body temperature is 37°C. A warm summer day in southern Europe is around 35°C.
Etymology: Named after Swedish astronomer Anders Celsius (1701–1744), who proposed a 100-degree scale in 1742. His original scale was inverted — 0°C meant boiling, 100°C meant freezing — and was reversed by fellow Swede Carl Linnaeus shortly after his death.
About Kelvin (K)
The kelvin (K) is the SI base unit of thermodynamic temperature. Unlike Celsius and Fahrenheit it has no degree symbol — temperatures are written "310 K", not "310°K". Kelvin is an absolute scale: 0 K is absolute zero, the theoretical lower bound of temperature where molecular motion effectively ceases. Since the 2019 SI redefinition, the kelvin is fixed by the Boltzmann constant (k = 1.380649 × 10⁻²³ J/K). Kelvin and Celsius share the same degree size — a change of 1 K equals a change of 1°C — making conversion straightforward: K = °C + 273.15. Kelvin is used in physics, chemistry, astronomy, and engineering thermodynamics.
The surface of the Sun is approximately 5,778 K. Liquid nitrogen boils at 77 K (−196°C). The cosmic microwave background temperature is 2.725 K.
Etymology: Named after William Thomson, 1st Baron Kelvin (1824–1907), the Irish-Scottish mathematical physicist who first proposed an absolute temperature scale in 1848. He was ennobled as Baron Kelvin of Largs in 1892, after the River Kelvin in Glasgow near where he worked.
Celsius – Frequently Asked Questions
Which countries use Celsius?
Almost every country in the world uses Celsius for everyday temperatures — weather forecasts, cooking, and body temperature. The United States, Liberia, and Myanmar are the principal exceptions, using Fahrenheit for daily life, though US scientists use Celsius for research.
What is absolute zero in Celsius?
Absolute zero — the theoretical minimum temperature where molecular motion effectively ceases — is −273.15°C. This corresponds to 0 K on the kelvin scale. It is not physically achievable but has been approached to within a few billionths of a degree in laboratory conditions.
How do you convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (or 1.8) and add 32. For example, 20°C × 1.8 + 32 = 68°F. A quick mental approximation: double the Celsius value and add 30 (gives ±2°F accuracy for typical weather temperatures).
What is normal body temperature in Celsius?
Normal human body temperature is approximately 37.0°C (98.6°F), though it varies by individual, time of day, and measurement site. A temperature above 38.0°C is generally considered a fever; hypothermia is diagnosed below 35.0°C.
What is the difference between Celsius and centigrade?
Centigrade is the old name for the same scale — both refer to a 100-degree span between water's freezing and boiling points ("centi" = 100, "grade" = step). The name was officially changed to Celsius in 1948 to avoid confusion with the angular unit also called "grade" (or "gradian") in some languages.
Kelvin – Frequently Asked Questions
How close to absolute zero have scientists actually gotten?
In 2021, researchers at the University of Bremen cooled rubidium atoms to 38 picokelvin (38 trillionths of a kelvin above absolute zero) inside a drop tower — the coldest temperature ever achieved. At these extremes, atoms form a Bose–Einstein condensate where quantum effects become visible at macroscopic scales. True 0 K is impossible to reach (the third law of thermodynamics forbids it), but each new record pushes closer, enabling research into superfluidity, quantum computing, and exotic states of matter.
Why do scientists use kelvin instead of Celsius?
Scientific calculations in thermodynamics, astrophysics, and chemistry require an absolute scale with no negative values. Many physical laws — the ideal gas law (PV = nRT), Wien's displacement law, Stefan–Boltzmann law — only work correctly with absolute temperature. Using Celsius would require constant offsets of 273.15.
What is the difference between kelvin and Celsius?
Kelvin and Celsius have identical degree sizes, so a temperature difference of 5 K equals a difference of 5°C. The only difference is the zero point: 0 K = −273.15°C. To convert: K = °C + 273.15. Kelvin has no negative values; Celsius does.
What everyday temperatures are expressed in kelvin?
Kelvin is rarely used in everyday life but appears in lighting (color temperature — a warm white bulb is around 3,000 K, daylight is 6,500 K), industrial processes, cryogenics (liquid helium: 4.2 K; liquid nitrogen: 77 K), and the specification of laser wavelengths and scientific instruments.
What is the coldest naturally occurring temperature in the universe?
The Boomerang Nebula, a protoplanetary nebula about 5,000 light-years away, has a measured temperature of approximately 1 K (−272°C), making it the coldest known naturally occurring place in the universe — colder than the cosmic microwave background (2.725 K).