F.C.K these temperature conversions

By: Bob Landstrom

Temperature and humidity are basic operational and service level metrics in the data centre world. American companies looking for data centre services outside of the United States, or companies looking for data centres within the United States will encounter this challenging mental mathematics of converting between temperature scales. It can be dizzying.

So what is it about these different temperature scales and why do we have them? Why can’t we all agree on just one? Who came up with this mess anyway?

Well, before jumping to the simple conversion formulae right away, let’s have a look at the history behind these ideas. Let’s begin with Fahrenheit, because this is the oldest of the three temperature scales.

F is for Fahrenheit

From the name, you correctly guess that Fahrenheit was German. Gabriel Daniel Fahrenheit was born in the late 17th century in Danzig. Just after the turn of the century in 1701, both of his parents died on the same day- victims of eating poisonous mushrooms. He then was sent to Amsterdam where he was an apprentice shop keeper. He became a physicist and a glass blower. Though living in Amsterdam, he traveled widely and became interested in making scientific instruments. By 1714, he had completed development of the mercury-in-glass thermometer.

The Fahrenheit temperature scale sets the freezing point of water at 32 degrees, and the boiling point of water at 212 degrees. To most observers, the selection of these numbers seems completely arbitrary. But why did he choose these numbers? How does this make any sense at all?

Fahrenheit noted that the boiling point of water varies with the change in atmospheric pressure. Depending on the weather or the altitude, the boiling point can be different. He also discovered that water could be super-cooled below its normal freezing temperature without it becoming ice. These observations led him to doubt the reliability of using the freezing and boiling points of water to measure temperature.

He found a truly stable freezing point of water with an equal parts mixture of water, ice and salt. This temperature marked the 0 degrees point of his scale. The 32 degree point marks the freezing of water and ice alone, and water boils at approximately 212 degrees when this scale is extended.

While his published work refers to use of freezing points of stable water and normal body temperature as the basis for his scale, some have theorised that Fahrenheit was a Freemason, and used 32 because of the degrees of enlightenment, and 212 being exactly 180 degrees out of phase with 32. I’m not aware of any records of him being a Freemason.

Later, his scale was adjusted slightly which made conversion to Celsius and Kelvin temperatures easier. This adjustment made the size of a Fahrenheit degree five-ninths the size of the same unit on the other two temperature scales. This enables exact measurements without using fractions with the Fahrenheit scale.

C is for Celsius

While his name sounds like a model of Japanese car, Anders Celsius was born in Uppsala, Sweden in 1701. His family pedigree was in science, astronomy, and mathematics. Anders chose a life in academics as well. His own early research was the first suggestion of the connection between the Aurora Borealis and the Earth’s magnetic field.

The work for which we all recognise Celsius is the 100-point scale for measuring temperature. He endeavored for a “centigrade” (meaning, 100 steps) scale between the freezing point and boiling points of water.

Interestingly, when first proposed, Celsius set the boiling point at 0 degrees and the freezing point at 100. Just after his death in 1744 another Swedish scientist, Carolus Linnaeus, reversed the scale for use in greenhouses, and a prominent instrument manufacturer began producing thermometers with that orientation. Because this was before modern communication technology, there are numerous scientists claiming creation of this same scale at that same time.

For quite a long time, it was simply called “the Swedish thermometer.” In 1948 most of the world adopted the Celsius scale as the standard for measuring temperature.

K is for Kelvin

William Thomson Kelvin was born in 1824 in Belfast, Ireland. While our earlier two engineer/physicists certainly had distinguished professional careers, they pale against that of Kelvin’s.

This guy was a scientific rock star. He was a distinguished mathematician and is responsible for unifying the then emerging field of physics. He had numerous inventions including a reliability improvement to the mariner’s compass, as well as contributions to electric telegraphy (not the least of which is the trans-Atlantic telecommunications cable). Knighted by Queen Victoria, he was the first scientist elevated to the House of Lords. Lord Kelvin did important work to formalise the first and second laws of thermodynamics which in fact, is an even better reason to include him in the data centre discussion. While we don’t typically deal with temperature in terms of Kelvin, thermodynamics is a fundamental element in data centre science.

Kelvin was also a pipe-smoker, so we have to love him for that.

Getting back to the temperature scale, a good deal of Kelvin’s thinking was about heat transfer between physical substances. He felt that thermometers of the day were useful as operational models, but did not adequately relate to what was really happening with the transfer of heat energy as a physical body cooled. This led to his creation of the absolute temperature scale, which worked independently of the physical properties of any body. Absolute zero is the temperature at which all thermal motion ceases.

Unlike the earlier two scales that we’re talking about here, Kelvin is not referred to as “degrees.” It is often used in conjunction with Celsius degree equivalents, but of itself is not typeset as a degree.

Which is better?

Today, only the US and a few Caribbean locations use the Fahrenheit scale. In 1975 the US made an attempt to standardise on SI units, but lacked the political will to enforce the conversion. Thus it was a voluntary move and still in the 21st century the US is using imperial measurement units and Fahrenheit for temperature. Working from the outside or from within the US entails this awkward conversion of scales.

To its credit, some have argued that the Fahrenheit scale has advantages over Celsius. For one, it allows for finer gradations of temperature in the ranges in which we all live and work. The only time we have to worry about the boiling point of water is when we’re cooking. It can be said too that the large degree ranges of temperature in the Fahrenheit scale map better to everyday life. For example, 30 degrees and below are frigid, 40’s to 50’s are sweater weather, 60’s to 70’s are comfortable, 90’s and up are hot as hell. A degree change on the Fahrenheit scale is a temperature that most people can detect themselves.

Celsius, on the other hand, just makes sense. Zero as freezing and 100 as boiling makes intuitive sense to most people. The majority of the Earth’s population seems to think so. Is it better than Fahrenheit? Well, they both measure the same thing so who’s to say. It’s just awkward that we have to make these mental conversions in the first place.

Temperature Conversions- The maths

Ok, you’ve suffered through my biographical obsessions. If you want to convert between these units of temperature, here are the formulae:


  from Fahrenheit  to Fahrenheit
Celsius  [°C] = ([°F] − 32) × 5⁄9  [°F] = ([°C] × 9⁄5) + 32
Kelvin  [K] = ([°F] + 459.67) × 5⁄9  [°F] = ([K] × 9⁄5) − 459.67


  from Celsius to Celsius
Fahrenheit  [°F] = ([°C] × 9⁄5) + 32 [°C] = ([°F] − 32) × 5⁄9
Kelvin [K] = [°C] + 273.15 [°C] = [K] − 273.15


  from Kelvin to Kelvin
Celsius [°C] = [K] − 273.15 [K] = [°C] + 273.15
Fahrenheit [°F] = ([K] × 9⁄5) − 459.67 [K] = ([°F] + 459.67) × 5⁄9