Overview

The Celsius scale, commonly called Celsius or historically centigrade, is a unit of measurement for temperature. Its values are expressed in degrees Celsius, written with the symbol °C. The scale is widely used in daily life, engineering and most scientific fields because of its convenient relation to the properties of water and its compatibility with the metric system.

Definition and key points

On the Celsius scale, the defining reference points are based on water under standard conditions: 0 °C is the melting (freezing) point of pure water and 100 °C is the boiling point of water at normal pressure (approximately sea-level atmospheric pressure). The interval between these two reference points is divided into 100 equal parts, so one degree Celsius represents one hundredth of that range. Because boiling point depends on pressure, the exact temperature at which water boils changes with altitude and local atmospheric conditions.

History and naming

The scale is named after the Swedish scientist Anders Celsius (1701–1744), a Swedish astronomer who proposed a centigrade scale in the 18th century. The early form of the scale was later inverted to place zero at the freezing point and 100 at the boiling point. The term "centigrade"—from Latin roots meaning "hundred steps"—was commonly used until 1948, when the International Committee for Weights and Measures adopted the name "Celsius" to avoid confusion with other uses of the word "grade."

Uses, examples and importance

The Celsius scale is the standard for weather reports, most national temperature regulations, cooking, and laboratory work. Typical examples of temperatures on the Celsius scale include human body temperature, seasonal averages, and industrial process temperatures. Its close relationship to the metric system simplifies calculations in science and engineering and makes it the preferred practical scale outside of a few countries that still commonly use Fahrenheit.

  • Everyday measurements (air and water temperatures)
  • Laboratory and industrial processes
  • Education and public health
  • Meteorology and climate reporting

Celsius is closely connected to the Kelvin scale, the SI unit for thermodynamic temperature: temperature in kelvins equals degrees Celsius plus 273.15. For common everyday conversions to the Fahrenheit scale the relationship is °F = °C × 9/5 + 32; Fahrenheit remains in use in some regions and contexts, so it is frequently compared with Celsius in mixed datasets and international communications. See also links on temperature measures: metric/SI and Fahrenheit.

Practical notes and notable facts

In scientific contexts that require absolute thermodynamic temperature, temperatures are expressed in kelvins rather than degrees Celsius. Practical effects such as the lowering of water's boiling point at high altitude illustrate why pressure matters for some Celsius reference points; the melting point of materials, calibration of instruments and precise laboratory work therefore specify pressure and purity conditions. For concise references to key concepts, see links on melting and boiling: melting point, boiling point.

For historical and biographical context regarding the scale's origin and creator, consult material about Anders Celsius and the early adoption of the centigrade concept: Anders Celsius and contemporary discussions of the concept as a scientific tool. Additional general resources include overviews of the nature of temperature and measurement conventions: unit of measurement, Swedish history, and broader educational summaries at standard pressure-related entries.