How this instrument works
Anders Celsius proposed his hundred-degree thermometer scale in 1742, but the version he published ran backwards by modern standards: zero for boiling water, one hundred for freezing. Within a couple of years, colleagues including the botanist Carl Linnaeus in Uppsala and, separately, the instrument maker Jean-Pierre Christin in Lyon flipped the orientation to the one everyone now takes for granted — zero at freezing, one hundred at boiling. That flipped, hundred-step scale is what the word centigrade came to mean, and it is identical to the Celsius scale used today.
The name itself is Latin arithmetic: centum for hundred, gradus for step, describing a scale divided into a hundred equal degrees between two fixed points. It stayed the common name for well over two centuries, appearing on thermometers, in textbooks and in weather forecasts worldwide, right up until an international standards body stepped in.
That step came in 1948, when the 9th General Conference on Weights and Measures formally renamed the unit degree Celsius, retiring degree centigrade from official use. Part of the reasoning was to honour the scale's own originator and part was to avoid a genuine clash: centigrade was already the name of an angular unit in some countries' surveying systems, one hundredth of a grade in a 400-grade circle, and having one word mean two unrelated things in scientific writing was an unnecessary hazard. The temperature scale itself never changed at all — only its official name did.
- Enter a reading into the Centigrade (°C) field — 20 is preloaded, a mild room temperature.
- Read the Celsius (°C) line beneath it; the number returned always matches what you typed, with no arithmetic applied.
- There is no reverse direction to worry about, since converting back gives you the identical figure you started with.
- If your source material predates 1948, or simply uses the older habit, treat any 'centigrade' figure exactly as you would a Celsius one — no adjustment required.
Worked example — a 20-degree reading needs no adjustment
An older textbook or an antique wall thermometer might mark its scale 'centigrade' rather than 'Celsius', and a reading of 20 on either one describes an identical temperature. Enter 20 into Centigrade (°C) and Celsius (°C) returns 20.0 — no shift, no scaling, because the two names have described one scale since the 1740s and one official name since 1948.
Contrast that with an actual conversion: 20 °C translates to 68 °F on the Fahrenheit scale, a real arithmetic step involving both a multiplication and an offset. Centigrade to Celsius involves neither. Anywhere you see 'centigrade' printed — an old recipe, a vintage oven dial, a European weather report from decades ago — you can substitute 'Celsius' directly and use every modern Celsius reference exactly as written.
Questions
Is centigrade the same as Celsius?
Yes, entirely — they name the same hundred-degree temperature scale, with water's freezing point at 0 and its boiling point at 100 under standard atmospheric pressure. Celsius became the scale's official name in 1948 by international agreement, replacing centigrade in formal use, but nothing about the scale's zero point or its degree size changed in that switch. Any centigrade figure can be read as a Celsius figure with no arithmetic at all.
Why was centigrade renamed to Celsius in the first place?
Two reasons converged in 1948, when the 9th General Conference on Weights and Measures made the change official. One was simple credit: naming the scale after Anders Celsius, who first proposed a hundred-degree thermometer scale in 1742. The other was practical — centigrade already named an angular unit, one hundredth of a grade, in some countries' surveying and engineering systems, and having the same word describe both a temperature and an angle invited genuine confusion in technical writing.
Did Anders Celsius invent the scale used today?
He proposed the idea in 1742, but his original version ran backwards from today's: zero marked boiling water, one hundred marked freezing. Within a few years, colleagues — commonly credited as Carl Linnaeus in Sweden and Jean-Pierre Christin in France, working independently — flipped the scale to the orientation everyone now uses. That corrected, hundred-step version is what later took the name Celsius.
Do any countries still officially call it centigrade?
No major standards body does today; Celsius has been the internationally recognised name since 1948. The word centigrade survives mainly in older documents, vintage instruments, casual speech and some historical or literary contexts, but every modern scientific, meteorological and engineering reference uses Celsius exclusively for this scale.
Is a centigrade degree the same size as a Celsius degree?
Yes, identically — there was never any change in scale, only in name. One degree centigrade and one degree Celsius both represent exactly one hundredth of the interval between water's freezing and boiling points at standard pressure, and both equal exactly one kelvin in size, since Celsius and Kelvin degrees are matched by definition and differ only in where their zero points sit.