# Celsius

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Conversion Formulae

The conversion formula for obtaining degrees celsius (°C) from kelvin (K) is as follows:

• °C = K - 273.15

The conversion formula for obtaining kelvin (K) from degrees celsius (°C) is as follows:

• K = °C + 273.15

The Kelvin temperature scale was created in response to the need for an absolute thermometric scale, it has its zero point at absolute zero and progresses from that point.

Kelvin is one of the seven base units of the SI system of units and a temperature interval of 1K is the same as a temperature interval of 1°C.

Celsius

Celsius is a temperature scale graduated in degrees that for many years was defined by the freezing point of water (0°C) and the boiling point of water (100°C). Until 1948 it was known as the centigrade scale because of the definition of 100 degrees from freezing to boiling water.

SI Metric

### Definition

The degree Celsius is defined as 1/273.16 of the difference between absolute zero and the triple point of water.

### Base Unit

Kelvin

Degrees Celsius have been defined in terms of Kelvin since 1954.

### Abbreviation

Formal: °C

The abbreviation deg C is also occasionally seen, often where the ° symbol cannot be printed/displayed. The abbreviation should always be written with the ° symbol next to the C and with a space after the number (e.g. 100 °C).

### Information

The Celsius temperature scale is named after the Swedish scientist Anders Celsius who developed a temperature scale based on the freezing point and boiling point of water with 100 units between the two in the early 1740's. Celsius published "Observationer om twänne beständiga Grader på en Thermometer" in 1742 defining the scales key points. The title translates as "Observations about two fixed degrees on a thermometer". Celsius's original scale had 0 degrees as the boiling point of water and 100 degrees as the freezing point - this scale was reversed, to the one we know today, by another Swedish scientist Carolus Linnaeus sometime before 1750.

The scale itself was called the centigrade scale until 1948 when the CIPM adopted the name Celsius to avoid confusion with a unit of angular measurement used by the Spanish and French.

In 1954 at the 10th Conférence Générale des Poids et Mesures (CGPM) the definition of the thermodynamic temperature scale was fixed with the triple point of a specific purified water being assigned the value of 273.16 Kelvin (with the interval of 1K being exactly 1 °C this effectively redefined the Celsius temperature scale). A further refinement to the definition was made at the 13th CGPM (1967/68).

Celsius is used as the primary day to day temperature scale across the world apart from in the United States, Belize, Palau and the United States territories of American Samoa and the US Virgin Islands.

### Conversion Formulae For Conversion To Celsius

• °C = K - 273.15
• 0 °C = 273.15K
• 100 °C = 373.15K

• °C = (°F - 32) x 5/9
• 0 °C = 32 °F
• 100 °C = 212 °F

• °C = (°R - 491.67) x 5/9
• 0 °C = 491.67 °R
• 100 °C = 671.67 °R

### Conversion Formulae For Conversion From Celsius

• K = °C + 273.15
• °F = (°C x 9/5) + 32
• °R = (°C + 273.15) x 9/5
Kelvin

The kelvin is a measurement unit for temperature defined by having its base at absolute zero, the temperature at which all thermal motion ceases. It is now one of the seven base units of the SI system of units.

SI Metric

### Definition

The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. This formal definition was Resolution 4 of the 13th CGPM (1967/68)

### Base Unit

Kelvin

The kelvin is one of the seven base units of the SI metric system.

### Abbreviation

Formal: K

The abbreviation degrees K or deg K were used prior to Resolution 3 of the 13th CGPM (1967/68), that formally defined the symbol K. (See Resolution 7 of the 9th CGPM (1948) and Resolution 12 of the 11th CGPM (1960) for more information.

### Information

The Kelvin scale is named after Northern Irish physicist and engineer William Thompson, 1st Baron Kelvin who identified the need for an absolute thermometric temperature scale in 1848.

Baron Kelvin used the accepted expansion coefficient of gas per degree Celsius (Centigrade in his time) relative to the ice point in order to calculate absolute zero - the base of the scale. His calculation gave a value of -273 °C.

In 1954 Resolution 3 of the 10th CGPM (1954) defined the scale using the triple point of water, with an assigned value of 273.16 K. This definition was further refined in 1967 at the 13th CGPM to the current formal definition.

Kelvin is used within the scientific community worldwide, including in the United States where Fahrenheit is still in everyday use for weather forecasts.

### Conversion Formulae For Conversion To Kelvin

• K = °C + 273.15
• 0 K = -273.15 °C

• K = (°F + 459.67) x 5/9
• 0 K = -459.67 °F

• K = °R x 5/9
• 0 K = 0 °R

### Conversion Formulae For Conversion From Kelvin

• °C = K - 273.15
• °F = (K x 9/5) - 459.67
• °R = K x 9/5
Common Conversions °C to K
 °C K 0 273.15 10 283.15 20 293.15 30 303.15 40 313.15 50 323.15 60 333.15 70 343.15 80 353.15 90 363.15 100 373.15
Common Conversions K to °C
 K °C 0 -273.15 100 -173.15 200 -73.15 300 26.85 400 126.85 500 226.85 600 326.85 700 426.85 800 526.85 900 626.85