My high school science teacher — a man who seemed old to me then and would seem reasonable to me now — always said “centigrade.” Years later I caught myself saying it to a younger relative, who looked at me the way you look at someone who calls the refrigerator an icebox.
Both names mean the same scale: water freezing at 0, boiling at 100 at standard pressure. So why are there two names, and is my old teacher’s version actually wrong?
The astronomer who built it upside down
The scale goes back to Anders Celsius, a Swedish astronomer who in 1742 proposed a thermometer with 100 steps between water’s boiling and freezing points. Here’s the detail I love: his original scale ran upside down by our standards — 0 marked boiling and 100 marked freezing.
It was flipped into the familiar orientation shortly afterward, with several people, including the botanist Carl Linnaeus, associated with the reversal. For about two centuries afterward, most of the world just called the result centigrade — Latin for “a hundred steps.” A perfectly sensible name.
Why centigrade had to go
The trouble was ambiguity. In French and Spanish, a centigrade (or centigrado) also referred to a unit of angle — one hundredth of a gradian. An international measurement system can’t tolerate one word meaning two different quantities in major languages.
So in 1948, the General Conference on Weights and Measures formally adopted the name degree Celsius, honoring the scale’s originator, following the same tradition that gave us the watt, the newton, and the kelvin. Officially, centigrade has been retired ever since — which means my teacher was out of date even when he taught me.
Old habits, and whether they’re wrong
Names fade slowly. British weather broadcasters kept saying centigrade for decades after 1948, and the word lives on in older textbooks, novels, and films. If someone says centigrade today, they’re not wrong about the temperature — 25 centigrade and 25 Celsius describe exactly the same afternoon. They’re just using a superseded label, a bit like calling Myanmar Burma.
A few formatting points worth knowing:
- The modern symbol is °C, with a space after the number in formal style: 25 °C
- Celsius keeps its degree sign; the kelvin, an absolute scale, does not
- One degree Celsius is exactly equal in size to one kelvin, by definition
The good idea underneath the name
Whatever you call it, the design remains one of metrication’s best moves: anchoring temperature to water’s two most familiar transformations makes the numbers intuitive anywhere water is part of daily life. Cooking, weather, and medicine all fit comfortably inside its 0-to-100 span. Even here in San Francisco, where the weather uses only a sliver of that range, the logic is hard to argue with.
If you meet centigrade in an old book — or hear it from an old teacher — just read it as Celsius: same scale, same numbers, older label.
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