A Heated Debate: Celsius vs Fahrenheit

Scale one or scale two? Which is better? Depends what you’re using them for. Here are ten good reasons why the Metric system has taken the world by storm—and twelve good reasons why the older, quainter, more exasperating English system of measurement is sometimes best.

An excerpt from Tying Down the Wind, by Eric Pinder
(Blackstone Audiobooks, 2002)

Most of the rest of the world now uses the Metric system. Except in the United States and Burma, Fahrenheit degrees have been replaced by Celsius, and units of distance like feet and miles appear almost as quaint as the obsolete stadia used by Eratosthenes in 200 B.C. In a way, that’s a shame.

The decimal metric system makes calculations simple—it makes numbers easier to juggle—and is likely to overcome resistance in the United States within a century. But the metric system is not perfect. The increasingly obsolete English system possesses a rustic charm and some surprising advantages. Fahrenheit degrees are more precise than Celsius degrees. And surely Robert Frost never would have written, “Kilometers to go before I sleep.” But let’s compare the two systems one unit at a time.

Distances & Weights

A fondness for the number 12 permeates the old English system of measurement. There are 12 inches to a foot, 12 units in a dozen, 12 dozen to a gross—even 12 pence to a shilling, in old British currency. To a mathematician with only ten fingers, the repetition of all those twelves can be maddening. (Just to make things even more confusing, there are 16 ounces in a pound; however, there were 12 ounces in the original Troy pound.)

The unit of distance called the foot, as its name suggests, was based on the length of a foot from heel to toe. The ancient Romans first divided it into increments of twelve. The Romans also invented the mile, defining it as the distance covered by one thousand paces. The Latin word mille means “a thousand.”

The problem, of course, was that no one’s foot or pace was exactly the same. With slightly more precision (and also a little arrogance) Kind Henry I of England in the year 1100 defined a “yard” as the distance between the tip of his nose and the end of his outstretched thumb. More than a century later, Edward I decided that a yard should equal three feet. Eventually, one mile became equal to 5280 feet.

Confusing? Yes. The metric system, by contrast, clears things up and is more practical. But despite its flaws, the convoluted English system of weights and measurements has entered the English language in a way that will take centuries to remove. “Give them an inch and they’ll take a mile,” will probably survive as an adage long after anyone remembers what an inch or a mile represent. Translate that sentence to “Give them a centimeter and they’ll take a kilometer,” and it lacks the same appeal.

“Inchworms” crawl along the leaves. A heavy object “won’t budge an inch.” And if you’ve ever found an idea hard to fathom, consider that a “fathom” originated as a nautical unit of depth equal to six feet. Today, most people use the word only as a verb, meaning “to understand.”

So even after it is fully supplanted by the metric system, the old English system is likely to linger in our everyday speech for many years to come.

Cold Facts about Temperature

Although the first real thermometer was invented in 1654, it was nothing but a unmarked tube of liquid that rose and fell as the temperature changed. No degrees or increments existed until 1701, when Isaac Newton suggested marking the tube “0” at the melting point of ice and (predictably enough, since Newton lived in England) 12 at body temperature.

In 1714, the German scientist Gabriel Fahrenheit replaced the existing water and alcohol thermometers with a mercury-based instrument. Not only did he improve the accuracy of thermometers, he expanded the range of the instrument (a water-based thermometer obviously cannot measure temperatures below the freezing point of water, and alcohol will boil on a hot summer day).

Fahrenheit set his “zero” at the lowest temperature he could create in his laboratory, which was equivalent to a fiercely cold winter night. At first he set body temperature equal to 12, as Newton had done. But Fahrenheit’s thermometers were so sensitive, he decided to divide his scale into much finer increments. Keeping zero where it was, the freezing point of water on the Fahrenheit scale turned out to be 32 degrees, and the boiling point of water, 212. The difference between the two was a perfect 180 degrees, a number easy to work with mathematically (half a circle, for instance, is 180 degrees of arc), so Fahrenheit was pleased.

In 1742, a Swedish astronomer named Anders Celsius created a new scale for the mercury thermometer. Celsius set the boiling point of water equal to zero and the freezing point at 100. (A year later he reversed these numbers, so that the temperature went up instead of down as heat increased.) The interval between freezing and boiling was thus a convenient 100 degrees. He called his invention the Centigrade scale, derived from the Latin for “a hundred steps.” Today the scale is named in honor of its inventor, and we speak of “degrees Celsius.”

Though most of the world uses the Celsius scale, the Fahrenheit scale may be better suited to everyday meteorology. For one thing, it is more precise and less coarse simply because each degree represents a smaller interval.

More importantly, the range in temperature from 0 to 100 degrees Fahrenheit closely demarcates the extremes found in the climates of the United States and Europe; it seldom gets much hotter. (The same range on the Celsius scale is a clumsier -18 to +38 degrees.)

However, the advantages of the Celsius scale in other aspects will win out in the end. (For instance, a Celsius degree is the same “size” as a degree Kelvin, making conversions and calculations much easier. Zero on the Kelvin scale equals absolute zero—the coldest temperature theoretically possible.) And so, in the future, a forecast of “ten degrees below zero” will not be as cold as it once was. I’m sure we’ll get used to it.


So, Is Celsius Better Than Fahrenheit?

If history had been a little different, we might be debating the merits of the (now obsolete) Réaumur scale today instead of Celsius versus Fahrenheit. In some parts of Europe, the Réaumur scale was once the Fahrenheit scale’s main rival.

In 1730, a French scientist named René Antoine Ferchault de Réaumur designed a scale in which the freezing point of water was set at 0 degrees. The boiling point was 80 degrees. Thermometers with Réaumur degrees were popular in France and most of Europe (though not in Britain) until supplanted by the metric system in the wake of the French Revolution in 1794.

Imagine we’re back in 1794 on an alternate Earth. People have suddenly realized, “Hey, metric is great, but we ought to have a temperature scale to go with it. So which shall we choose?” Any scale, including Fahrenheit or Celsius or even Réaumur, can be linked to the metric system with equal ease. The Celsius scale is not really “metric” in the same practical way that, say, centimeters and kilometers are. You can quickly and easily find out how many centimeters are in 1.36 kilometers, unlike inches and miles. (Quick! How many inches in 1.36 miles?) But when it comes to temperature scales, doing the math is just as easy in Fahrenheit as it is in Celsius. Had Gabriel Fahrenheit lived in France and Anders Celsius in Britain, it might have been the Fahrenheit scale which was “attached” to the metric system instead of vice versa.

Lord Kelvin (William Thomson) forever linked the Celsius scale into the metric system by using Celsius-sized degrees. But he could just as easily have made his scale start at absolute zero using Fahrenheit- or Réaumur-sized degrees. (The Rankine scale also starts at absolute zero, a la Kelvin, but uses Fahrenheit-sized degrees. Kelvin and Rankine are equal at absolute zero. The point at which Celsius and Fahrenheit are equal is -40 degrees C or F.)

The scientific community adopted Kelvin instead Rankine, and that pretty much sealed the deal for Celsius. Today’s familiar units such as joules and the calorie (the amount of energy needed to raise the temperature of a gram of water by 1˚C) assume we’re working with Celsius-sized degrees. There’s even a new diet soft drink called Celsius, playing off of the calorie/weight loss connection. We could just as easily have defined the calorie using Fahrenheit-sized degrees (though there’d be more “calories” in your milkshake, and you’d burn more calories on your daily walk). But it’s too late to change now.

What follows is my personal opinion. After becoming “fluent” in both Celsius and Fahrenheit during my seven years at the Mount Washington Observatory, I’ve reached three conclusions.

Both scales have certain advantages.
All of those advantages are so trivial as to be negligible.
For talking about everyday weather, I find Fahrenheit slightly superior.

There’s no question that the metric system (or rather, the Système International d’Unités) is far superior to the English system in terms of ease of calculation and unit conversion. But I suspect many people let their enthusiasm for metric carry over automatically to Celsius (which is not necessarily superior) just because, hey, Celsius is attached to the metric system and metric is best.

Celsius has one advantage over Fahrenheit. The argument boils down to this: “Zero is freezing, 100 is boiling, and that’s nice and easy to remember if you need to bring in your plants off the balcony before they freeze.”

I find that somewhat weak. If you can remember half a dozen passwords and phone numbers without any problem, I don’t buy the argument that it’s a challenging burden to remember a single number like 32˚F. It’s not even universally true. Zero and 100˚C are not the melting/boiling points of water on, say, the surface of Mars. Even on Earth, they vary with salinity and pressure/altitude.

When we’re talking about temperature, we’re usually talking about comfort level, which is what Gabriel Fahrenheit originally based his scale on. 100˚F was meant to be human body temperature. Okay, Gabe missed by just a bit. But body temperature varies individually in any case, and slight fevers above 100 are not uncommon, so this doesn’t bother me. In general, “Temperature will rise into the triple digits today!” means the outside air will be warmer than your internal body temperature. It’s the point at which your body becomes a heat sink instead of a heat source. In terms of comfort, that’s very significant and not at all arbitrary. (It’s also remains true regardless of salinity or pressure or, for that matter, what planet you’re on.)

Base 10

So, we have Celsius, where 0 degrees is the melting point of water and 100 degrees is the boiling point (which is so far off the charts that it’s just not a factor when talking about everyday weather). And we have Fahrenheit, where 0 degrees represents the coldest point Gabriel Fahrenheit could create in his laboratory (pretty arbitrary) and 100 degrees is his rough approximation of human body temperature. Fahrenheit degrees are smaller than Celsius degrees. Or, to put it another way, Celsius degrees have a lower resolution and are less precise.

“Less precise?” you might ask. “Why not just use decimal points?” Many people do. To understand the centigrade scale, remember this little rhyme:

Zero is freezing, 10 is not.
20 is pleasant, 30 is hot.

But it’s clumsier to communicate using decimal points in ordinary conversation, and especially while broadcasting weather reports. Which is why that clever little rhyme doesn’t say, “Zero is freezing, 10.1 is not, 19.8 is pleasant, 30.4 is hot.”

Think about a truly decimal “0 = freezing, 10 = boiling” scale. If someone tried to impose that scale on us and started saying things like, “What’s the problem? It’s easy. Zero is freezing, one is not, two is pleasant, three is hot. If you need more precision, just use decimal points,” I doubt they’d be taken very seriously.

Officially, weather stations in the US used to record temperatures to the nearest tenth of a degree Fahrenheit, every one or three hours. These days the official records are in Celsius (though cloud heights are still in feet, oddly). Does that make much of a difference? Probably not. But it is a slight loss in resolution.

The bottom line is that both Fahrenheit and Celsius have units (degrees) in base 10, and are just as easy to calculate with. With meters/kilometers vs miles/inches, the metric system in indisputably superior. (“How many inches in 1.54 miles?” gives me a headache.) But that’s just not a factor when it comes to Fahrenheit vs Celsius. In a practical sense, Celsius is no more “metric” than Fahrenheit. 

Talking about Weather

If you live outside the United States, you’re probably not used to thinking in or communicating with Fahrenheit. I used to “talk weather” all day, both on the air and in classroom settings. In casual conversation, I found I could communicate information more quickly and with more nuances in Fahrenheit than in Celsius. It’s subtle, and probably has something to do with how humans process language. There are simply a greater number of phrases that can be used to convey subtly different meanings to listeners who are “fluent” in Fahrenheit.

The advantage is trivial, and unless you’re a linguist or a meteorologist or a weather nerd, probably all but unnoticeable. But it’s there.

I think the U.S. and the rest of the world should come to a compromise. We in the U.S. will finally get rid our clunky miles and gallons and replace them with the more sensible kilometers and liters, if everyone else replaces Celsius with Fahrenheit. But that has about as much chance of happening as the 24-hour day being replaced worldwide by “metric” time. Alas.

More Resources:

This useful site will convert temperatures between all five scales, including Kelvin, Rankine, and even Réaumur

A common, comfortable room temperature is
20 degrees C = 68 degrees F = 16 degrees Réaumur = 293.15 Kelvin = 527.67 degrees Rankine

Going by the rhyme above, “hot” is

30 degrees C = 86 degrees F = 24 degrees Réaumur = 303.15 Kelvin = 545.67 degrees Rankine

You’ll notice I didn’t say “degrees Kelvin” or use the degree symbol (°) the way I did with Fahrenheit and Celsius. The convention is that you don’t say “273 degrees Kelvin,” just “273 Kelvin.”

When it’s -40 degrees outside, it doesn’t matter which temperature scale you use. (Fahrenheit and Celsius are equal at this point.)

For more weather musings, see
Life at the Top

Celsius to Fahrenheit Conversion Formula

To convert Fahrenheit to Celsius, subtract 32, then multiply the result by 5/9ths (or 0.5555).


50 degrees F minus 32 = 18

18 times 0.5555 = 10 degrees C


To convert Celsius to Fahrenheit, first multiply by 9/5ths (or 1.8), then add 32 to the result.

10 C times 1.8 = 18

18 + 32 = 50 F

Compare common temperatures:

100 F = 38 C

80 F = 27 C

40 F = 4 C

32 F = 0 C

-20 F = -28 C

-40 F = -40 C
(The two scales are equal at this point.)

-60 F = -51 C


Temperature Records and Extremes

136 F = 58 C
(Highest temperature on Earth, el-Aziziah,   Libya, 1922.)

134 F = 56 C
(Hottest temperature in United States, Death Valley, 1913.)

-79.8 F  = -62 C (Coldest temperature in United States, Prospect Creek, Alaska, 1971.)

-128.6 F = -89 C (Coldest temperature on Earth, Vostok     Station Antarctica, 1983.)