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Clouds wash over Mount Katahdin's Tablelands, just a mile or so from the northern terminus of the Appalachian TrailNin the cat on Mount Washington. Illustration by T.B.R. Walsh from Cat in the Clouds

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An old fashioned thermoshackA 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) Listen to another free 12-minute excerpt from the audiobook: a scene set at the Mount Washington Observatory on a cold, hurricane-force day. Click here, then click the green button under the cover on the following page.

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 Except in the United States and Burma, Fahrenheit degrees have been replaced by Celsius, and units of distance like feet and miles appear almost as quaint as the obsolete stadia used by Eratosthenes in 200 B.C. In a way, that’s a shame.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—in short, it makes it easier to juggle numbers—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 in the British unit of currency, the shilling. 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.



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 meteorology. For one thing, it is more precise and less coarse simply because each degree represents a smaller interval.

Speaking of extreme weather....the famous, frosty Mount Washington weather cats appear in a colorful new children’s book.

Cat in the Clouds on Facebook

More importantly, the range in temperature from 0 to 100 degrees Fahrenheit almost perfectly demarcates the extremes found in the climates of the United States and Europe; it seldom gets any hotter or colder. The convenience of a perfect 100 degree interval encompassing the temperatures in which most of us live seems a pity to lose. (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.

Continued - More opinions about Celsius vs Fahrenheit vs Réaumur.

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.)


Click to learn more about weather in this exclusive interview with Don Kent, Boston’s first TV weatherman.

Find this weather coffee mug and other meteorology gifts at Two Wheels Good.

What’s a typical day like for a meteorologist? Tag along from dawn to dusk with the weather observers at the Mount Washington Observatory as they de-ice the thermoshack, read radio forecasts, rescue lost hikers and, yes, convert Fahrenheit to Celsius.

 A Day in the Life of a Weather Observer. Caution: long day ahead


Reference Book Recommendation


Measurements & Conversions: A Complete Guide is a pocket-sized volume of useful information, including Celsius to Fahrenheit and Metric to English converstions, UK, US and European shoe size and clothing size converstion tables, lists of the highest volcanoes and highest mountains, deepest caves, life expectancies, historic number systems, lists of prime numbers, the Fibonacci sequence, and more. There’s even a perpetual calendar. All inside a tiny book that fits in the palm of your hand. Like Doctor Who’s TARDIS, it’s bigger on the inside than the outside.

Unfortunately, it’s also out of print. But you can still find used copies at the link to the right.

I keep a copy on top of my computer speaker, within easy reach.

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




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Text and photographs © Eric Pinder