- deg C
- degree C
The Celsius scale, already widely used in Europe, replaced the Fahrenheit scale in most countries during the mid-to-late 20th century, although Fahrenheit remains the official scale of the United States, Cayman Islands and Belize.
Although initially defined by the freezing point of water (and later the melting point of ice), the Celsius scale is now officially a derived scale, defined in relation to the Kelvin temperature scale.
Zero on the Celsius scale (0 °C) is now defined as the equivalent to 273.15 K, with a temperature difference of 1 deg C equivalent to a difference of 1 K, meaning the unit size in each scale is the same. This means that 100 °C, previously defined as the boiling point of water, is now defined as the equivalent to 373.15 K.
The Celsius scale is an interval system but not a ratio system, meaning it follows a relative scale but not an absolute scale. This can be seen because the temperature interval between 20 °C and 30 °C is the same as between 30 °C and 40 °C, but 40 °C does not have twice the air heat energy of 20 °C.
A temperature difference of 1 deg C is the equivalent of a temperature difference 1.8°F.
The Celsius scale is named after the Swedish astronomer Anders Celsius (1701-1744). In 1742, Celsius created a temperature scale wherein 0 degrees was the boiling point of water and 100 degrees the freezing point.
Around this time other physicists independently developed a similar scale but reversed, such that 0 degrees was the melting point of ice and 100 degrees the boiling point of water. This new ‘forward’ scale was widely adopted across continental Europe, generally being referred to as the centigrade scale.
The scale was officially named as ‘The Celsius scale’ in 1948 to prevent confusion with the use of centigrade as an angular measurement.
- Absolute Zero, -273.15 °C
- Melting point of ice, 0 °C (actually -0.0001 °C)
- Warm summer's day in a temperate climate, 22 °C
- Normal human body temperature, 37 °C
- Boiling point of water at 1 atmosphere, 99.9839 °C