Temperature Scales: Fahrenheit and Celsius

The two primary temperature scales of Celsius and Fahrenheit side-by-side calling out water freezing, body temperature and water boiling

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It's remarkable to think that for most of human history, there was no standard way to describe how hot or cold something was. The invention of temperature scales made it possible to quantify temperature in science, medicine, and daily life.

The two most widely used temperature scales worldwide are the Celsius and Fahrenheit scales. Most of the world uses the Celsius scale. The US is the main, though not the only, user of the Fahrenheit scale.

What is the Celsius Scale?

The Celsius scale, named after Swedish astronomer Anders Celsius, sets 0°C at the freezing point of water and 100°C at the boiling point of water at standard atmospheric pressure (sea level).

What is the Fahrenheit Scale?

The Fahrenheit scale sets 32°F as the freezing point of water and 212°F as the boiling point, creating a span of 180°F between the two. This means that each degree Celsius equals 1.8 degrees Fahrenheit.

There are several stories about how Daniel Fahrenheit developed the scale. The general idea is that he chose:

0°F at the freezing point of a salty brine solution
32°F at the freezing point of pure water
and another point at body temperature around 96F (now 98.6F)

He divided up the scale between these points, giving a scale with helpful resolution and practical reference points.

Quick Tricks to Convert Between Fahrenheit and Celsius

Having lived on both sides of the Atlantic, I've tried to get somewhat familiar with both temperature scales. To convert between them in my head, at least around most air temperatures, I use a quick approximation.

To go from Fahrenheit to Celsius

Subtract 32, then divide by 2 (or slightly less for better accuracy)

As 32°F is 0°C, and for each one Celsius you move almost two Fahrenheit, you can roughly go from Fahrenheit to Celsius by subtracting 32 and dividing by 2 (or a little less to be closer). So, for example:

50°F is approximately 9°C (actually 10°C),
86°F is approximately 27°C (actually 29.4°C).

To go from Celsius to Fahrenheit

Use the reverse: Multiply by 2 and add 32.

10°C --> 52°F (actually 50°F)
30°C --> 92°F (actually 86°F)

It's not perfect, but it's often good enough if you need to work out if it'll be hot out.

Temperature Twins

There are also at least two simple anchor points that can help just by swapping the digits around:

82°F is near enough 28°C
61°F is near enough 16°C

Not only do they mirror each other visually, but the conversions are surprisingly accurate.

The Kelvin Scale

Both Fahrenheit and Celsius are now defined relative to the Kelvin scale—a temperature scale used in science that sets absolute zero (0 K) as the lowest possible temperature, where molecular motion essentially stops.

Zero on the Kelvin scale is around -273°C. As such, the Kelvin scale, though helpful for scientists, is not very practical for discussing the weather.

Related Ideas to Temperature Scales

The Fun Scale: three types of fun
The Bortle Scale: the clarity of the night sky
The Scoville Scale: chilli heat
The Goldilocks Zone: the circumstellar habitable zone just right to support liquid water
Heat Islands: urban areas with higher temperatures than surrounding rural areas with more greenery
Weather and Climate: an analogy
It's not the Weather, it's the Unpredictability
Word Spectrums

Published 5 Feb 2023

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An eponym is a word named after somebody or someplace. An eponym, almost by definition, comes with a story, making them some of the most intriguing words. Knowing what an eponym is also allows you to use the word eponymous, which is always a good way to sound smart. Some of my favourite eponyms are now commonplace products that took the inventor's name. Some examples: The Rubik's Cube The Rubik's cube is an invention by Hungarian architecture professor Ernő Rubik. The cube has the fascinating property of being a solid object that's also fluid. This year (2024), the Rubik's Cube turned 50, celebrating around half a billion cube sales, scores of speed-cubing championships, and documentaries. When Rubik first invented the cube, he wasn't sure it was solvable and only managed it for the first time several months after creating it. In 2020, Rubik told the story of the cube in his book, Cubed: The Puzzle of Us All. The Jacuzzi The fabulously named jacuzzi, or more generally the hot tub, is named after the Italian Jacuzzi family. The seven brothers of the family—there were also six daughters—trained to become engineers, making plane propellers, irrigation systems and pumps before one of the brothers created a homemade bath to help his two-year-old son who was suffering from rheumatoid arthritis. The rest, as they say, is history. Saskia Solomon tells some of the brothers' story, which includes the court case Jacuzzi vs Jacuzzi, and the invention of the jacuzzi in the 2023 New York Times article, The Frothy Saga of the Jacuzzi Family. The Sandwich After so long as what seems the most basic of foods, it was remarkable for me to learn that the humble sandwich was named after a person: John Montague, the 4th Earl of Sandwich. Though he probably spent most of his time in London, the title itself is associated with the small town of Sandwich in Kent, in Southeast England. The story goes that the Earl liked playing cards and wanted food he could eat without having to leave his game and that wouldn't give him sticky fingers that would damage the cards. Incarnations of open sandwiches appeared much earlier elsewhere. For example, the trencher—something I had to look up when reading Game of Thrones—involved serving food on top of old bread as a sort of plate. But it took the Earl's dedication to card playing, or at least desk work, to take the next step many years later. The Biro and BiC ballpoint pens László Bíró was a Hungarian-Argentine inventor who created the first truly successful ballpoint pen. In the US, the BiC is more common, an eponym this time from Marcel Bich. It's said that Lázló experienced his fountain pen leaking from heat—fountain pens being very common before the ballpoint—and was inspired by a printing press that used a cylinder to spread the ink. All it needed was to go in all directions. Enter the ballpoint. While the invention seems obvious in hindsight, perfecting it for robust, commercial use was challenging. For example, finding suitable ink for the tiny ball bearing to spread, which doesn't leak or clog and isn't overly affected by heat. Lázló teamed up with an aviation company—who use a lot of ball bearings—which also provided a great use case of finding a pen that wouldn't leak from the air pressure changes in planes. Later, BiC licenced the technology from Biro. A Bic Cristal® Ballpoint pen is part of the collection at the MoMA. Silhouette I only learned that silhouette was an eponym while preparing this sketch, but it's perhaps the best of all. Étienne de Silhouette, a French government finance official tasked with curbing a French deficit in the 1700s, unwittingly gave his name to the classic black-on-white simple outline image of a person. His severe frugal policies of taxes, curbing royal spending and even melting down gold and silverware earned him the reputation of doing things cheaply. Hence, a cheap method of creating a portrait, cutting out black paper and laying it on a white background, became known as a silhouette. Diesel Nearly everyone will recognise the fuel that Rudolf Diesel gave his name to and his diesel engine. Diesel created a breakthrough engine that was more efficient than typical steam engines while being smaller and weighing less. Curiously, I learned that Diesel died in mysterious circumstances, disappearing on a journey across the English Channel in 1913. -- An excellent episode of the 99% Invisible podcast featuring Helen Zaltzman of the Allusionist raised several interesting questions about eponyms I hadn't considered. Here are a few to think about: Eponyms are common in medicine, for example, when we name a disease or condition after those playing a part in the discovery. However, the name, for example, Creutzfeldt-Jakob disease, tells a medical practitioner very little about the disease compared to a name that relates to the symptoms of the sufferer or the cause. Should examples like these be replaced with more practical names? Eponyms almost always have a way of oversimplifying a story, often wrapping up complex histories with the names of white males. For example, rarely are products invented or diseases identified solely through the actions of one person. Yet an eponym chooses one, or some people, at the expense of others. Eponyms may be the name of someone later discredited or who develops a tarnished reputation from other actions in their lives. Should someone who did evil deeds be remembered in an eponym or should it be changed? Who knew eponyms could be so interesting? Know some good eponyms with fun stories? I'd love to hear them. Eponyms are distinct from the fun concept of Nominative determinism—an aptronym—where someone's name seemingly influenced their future actions or career choices (for example, Les McBurney — Volunteer firefighter). I've covered a lot of eponyms over the years, far more than I realised. Using the handy list page on the site, I've collected some other eponym examples, which include a lot of my favourites: Bloom's Taxonomy Bortle Scale Braille Campbell's law Chesterton's fence Conway's Law Dracula sneeze Dunbar's number: 150 Fahrenheit and Celsius Fitts' Law Goldilocks tasks Goodhart's Law Hanlon's Razor Hofstadter's Law Identify a Douglas fir Jevon's Paradox Johari window Koomey's Law The Kano model Marchetti's constant Maslow's hierarchy of needs Metcalfe's Law Möbius strip Moore's Law Muphry's Law Pyrrhic victory Russell's Teapot Sankey diagram Scoville scale Spoonerisms Strahler stream order The Abilene paradox The Barnum effect The Betty Crocker Effect The Boaty McBoatface effect The Diderot Effect The Doppler Effect The Droste effect The Feynman Learning Technique The Gartner Hype cycle The Generalised Peter Principle The Gini coefficient The Goldilocks Zone The IKEA effect The Keeling curve The Lake Wobegon Effect The Lucretius problem The Mercator projection The Monty Hall problem The Overton Window The Oxford comma The Peter Principle The Plimsoll line The Pomodoro Technique ® The Rashomon effect The Rosetta Stone The Shirky Principle The Streisand Effect The Stroop test Veblen goods Other fun -onym words about words: Acronyms and initialisms Capitonym Heteronym Homonyms, homographs, homophones… An eponym is a word named after somebody or someplace. An eponym, almost by definition, comes with a story, making them some of the most intriguing words. Knowing what an eponym is also allows you to use the word eponymous, which is always a good way to sound smart. Some of my favourite eponyms are now commonplace products that took the inventor's name. Some examples: The Rubik's Cube The Rubik's cube is an invention by Hungarian architecture professor Ernő Rubik. The cube has the fascinating property of being a solid object that's also fluid. This year (2024), the Rubik's Cube turned 50, celebrating around half a billion cube sales, scores of speed-cubing championships, and documentaries. When Rubik first invented the cube, he wasn't sure it was solvable and only managed it for the first time several months after creating it. In 2020, Rubik told the story of the cube in his book, Cubed: The Puzzle of Us All. The Jacuzzi The fabulously named jacuzzi, or more generally the hot tub, is named after the Italian Jacuzzi family. The seven brothers of the family—there were also six daughters—trained to become engineers, making plane propellers, irrigation systems and pumps before one of the brothers created a homemade bath to help his two-year-old son who was suffering from rheumatoid arthritis. The rest, as they say, is history. Saskia Solomon tells some of the brothers' story, which includes the court case Jacuzzi vs Jacuzzi, and the invention of the jacuzzi in the 2023 New York Times article, The Frothy Saga of the Jacuzzi Family. The Sandwich After so long as what seems the most basic of foods, it was remarkable for me to learn that the humble sandwich was named after a person: John Montague, the 4th Earl of Sandwich. Though he probably spent most of his time in London, the title itself is associated with the small town of Sandwich in Kent, in Southeast England. The story goes that the Earl liked playing cards and wanted food he could eat without having to leave his game and that wouldn't give him sticky fingers that would damage the cards. Incarnations of open sandwiches appeared much earlier elsewhere. For example, the trencher—something I had to look up when reading Game of Thrones—involved serving food on top of old bread as a sort of plate. But it took the Earl's dedication to card playing, or at least desk work, to take the next step many years later. The Biro and BiC ballpoint pens László Bíró was a Hungarian-Argentine inventor who created the first truly successful ballpoint pen. In the US, the BiC is more common, an eponym this time from Marcel Bich. It's said that Lázló experienced his fountain pen leaking from heat—fountain pens being very common before the ballpoint—and was inspired by a printing press that used a cylinder to spread the ink. All it needed was to go in all directions. Enter the ballpoint. While the invention seems obvious in hindsight, perfecting it for robust, commercial use was challenging. For example, finding suitable ink for the tiny ball bearing to spread, which doesn't leak or clog and isn't overly affected by heat. Lázló teamed up with an aviation company—who use a lot of ball bearings—which also provided a great use case of finding a pen that wouldn't leak from the air pressure changes in planes. Later, BiC licenced the technology from Biro. A Bic Cristal® Ballpoint pen is part of the collection at the MoMA. Silhouette I only learned that silhouette was an eponym while preparing this sketch, but it's perhaps the best of all. Étienne de Silhouette, a French government finance official tasked with curbing a French deficit in the 1700s, unwittingly gave his name to the classic black-on-white simple outline image of a person. His severe frugal policies of taxes, curbing royal spending and even melting down gold and silverware earned him the reputation of doing things cheaply. Hence, a cheap method of creating a portrait, cutting out black paper and laying it on a white background, became known as a silhouette. Diesel Nearly everyone will recognise the fuel that Rudolf Diesel gave his name to and his diesel engine. Diesel created a breakthrough engine that was more efficient than typical steam engines while being smaller and weighing less. Curiously, I learned that Diesel died in mysterious circumstances, disappearing on a journey across the English Channel in 1913. -- An excellent episode of the 99% Invisible podcast featuring Helen Zaltzman of the Allusionist raised several interesting questions about eponyms I hadn't considered. Here are a few to think about: Eponyms are common in medicine, for example, when we name a disease or condition after those playing a part in the discovery. However, the name, for example, Creutzfeldt-Jakob disease, tells a medical practitioner very little about the disease compared to a name that relates to the symptoms of the sufferer or the cause. Should examples like these be replaced with more practical names? Eponyms almost always have a way of oversimplifying a story, often wrapping up complex histories with the names of white males. For example, rarely are products invented or diseases identified solely through the actions of one person. Yet an eponym chooses one, or some people, at the expense of others. Eponyms may be the name of someone later discredited or who develops a tarnished reputation from other actions in their lives. Should someone who did evil deeds be remembered in an eponym or should it be changed? Who knew eponyms could be so interesting? Know some good eponyms with fun stories? I'd love to hear them. Eponyms are distinct from the fun concept of Nominative determinism—an aptronym—where someone's name seemingly influenced their future actions or career choices (for example, Les McBurney — Volunteer firefighter). I've covered a lot of eponyms over the years, far more than I realised. Using the handy list page on the site, I've collected some other eponym examples, which include a lot of my favourites: Bloom's Taxonomy Bortle Scale Braille Campbell's law Chesterton's fence Conway's Law Dracula sneeze Dunbar's number: 150 Fahrenheit and Celsius Fitts' Law Goldilocks tasks Goodhart's Law Hanlon's Razor Hofstadter's Law Identify a Douglas fir Jevon's Paradox Johari window Koomey's Law The Kano model Marchetti's constant Maslow's hierarchy of needs Metcalfe's Law Möbius strip Moore's Law Muphry's Law Pyrrhic victory Russell's Teapot Sankey diagram Scoville scale Spoonerisms Strahler stream order The Abilene paradox The Barnum effect The Betty Crocker Effect The Boaty McBoatface effect The Diderot Effect The Doppler Effect The Droste effect The Feynman Learning Technique The Gartner Hype cycle The Generalised Peter Principle The Gini coefficient The Goldilocks Zone The IKEA effect The Keeling curve The Lake Wobegon Effect The Lucretius problem The Mercator projection The Monty Hall problem The Overton Window The Oxford comma The Peter Principle The Plimsoll line The Pomodoro Technique ® The Rashomon effect The Rosetta Stone The Shirky Principle The Streisand Effect The Stroop test Veblen goods Other fun -onym words about words: Acronyms and initialisms Capitonym Heteronym Homonyms, homographs, homophones…

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