# Celsius

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Conversion Formulae

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

• °C = (°F - 32) x 5/9

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

• °F = (°C x 9/5) + 32

Using these formulae the freezing point of water 0 °C is 32 °F and the boiling point of water 100 °C is 212 °F.

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
Fahrenheit

The Fahrenheit temperature scale is a non SI temperature scale that is now based on two fixed points, the freezing point of water at 32 °F and the boiling point of water 100 °F.

US Customary

### Definition

1 degree fahrenheit is 1/180th of the interval between the freezing point and boiling point of water. The scale is defined by the freezing point of water at 32 °F and the boiling point of water at 212 °F.

### Base Unit

Fahrenheit

The fahrenheit temperature scale is used in US Customary units and was formerly used in British Imperial units as the main unit of temperature.

Formal: °F

### Information

The Fahrenheit temperature scale is names after Daniel Fahrenheit, inventor of the mercury thermomenter, who first proposed the scale in 1724.

Fahrenheit's original scale wasn't based around the freezing and boiling points of water. Some stories say it was based on the lowest temperature to which Farhenheit could reproducibly cool brine (0 degrees) and the average human body temperature (100 degrees), though these would appear to be strange reference points and given that serious research on average human body temperature wasn't done until the 19th century fairly unlikely to be true.

Other sources link the work of Fahrenheit to earlier work done by Ole Rømer, whose temperature scale was based on the freezing point of brine and the boiling point of water.

The Fahrenheit temperature scale was used widely around the world until the mid to late 20th Century when many countries that had previously used Fahrenheit, such as the United Kingdom, Canada, India and Australia, adopted the SI metric Celsius temperature scale.

Fahrenheit is used in the United States of America, the Bahamas, Belize, the Cayman Islands and US Territories such as Guam, Puerto Rico and the US Virgin Islands.

### Conversion Formulae For Conversion To Fahrenheit

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

• °F = (K x 9/5) - 459.67
• 32 °F = 273.15 K
• 212 °F = 373.15 K

• °F = °R - 459.67
• 32 °F = 491.67 °R
• 212 °F = 671.67 °R

### Conversion Formulae For Conversion From Fahrenheit

• °C = (°F - 32) x 5/9
• K = (°F + 459.67) x 5/9
• °R = °F + 459.67
Common Conversions °C to °F
 °C °F -29 -20.20 -28 -18.40 -27 -16.60 -26 -14.80 -25 -13.00 -24 -11.20 -23 -9.40 -22 -7.60 -21 -5.80 -20 -4.00
 °C °F -19 -2.20 -18 -0.40 -17 1.40 -16 3.20 -15 5.00 -14 6.80 -13 8.60 -12 10.40 -11 12.20 -10 14.00
 °C °F -9 15.80 -8 17.60 -7 19.40 -6 21.20 -5 23.00 -4 24.80 -3 26.60 -2 28.40 -1 30.20 0 32.00
 °C °F 1 33.80 2 35.60 3 37.40 4 39.20 5 41.00 6 42.80 7 44.60 8 46.40 9 48.20 10 50.00
 °C °F 11 51.80 12 53.60 13 55.40 14 57.20 15 59.00 16 60.80 17 62.60 18 64.40 19 66.20 20 68.00
 °C °F 21 69.80 22 71.60 23 73.40 24 75.20 25 77.00 26 78.80 27 80.60 28 82.40 29 84.20 30 86.00
 °C °F 31 87.80 32 89.60 33 91.40 34 93.20 35 95.00 36 96.80 37 98.60 38 100.40 39 102.20 40 104.00
Common Conversions °F to °C
 °F °C -50 -45.56 -45 -42.78 -40 -40.00 -35 -37.22 -30 -34.44 -25 -31.67 -20 -28.89 -15 -26.11 -10 -23.33 -5 -20.56
 °F °C 0 -17.78 5 -15.00 10 -12.22 15 -9.44 20 -6.67 25 -3.89 30 -1.11 35 1.67 40 4.44 45 7.22
 °F °C 50 10.00 55 12.78 60 15.56 65 18.33 70 21.11 75 23.89 80 26.67 85 29.44 90 32.22 95 35.00