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50 free Celsius trivia questions with answers — science & nature quiz, new questions added Aug 2026.
Celsius trivia begins with a surprise: the Swedish astronomer who proposed the scale in 1742 put boiling water at 0 and freezing at 100, and it took a French physicist and Carl Linnaeus to turn it the right way up. The name 'centigrade' survived until 1948, when it was dropped partly because it also meant a hundredth of a right angle in French. This quiz covers Anders Celsius himself (Uppsala, the aurora, the Lapland expedition), the history of the scale, the difference between a temperature and an interval, why the boiling point of water is no longer exactly 100 °C, the kelvin and absolute zero at −273.15 °C, Daniel Fahrenheit's brine and body-heat fixed points, the −40 crossover, the Réaumur and Rankine scales, the triple point of water, the 2019 Boltzmann-constant redefinition, and the handful of countries where Fahrenheit still rules the weather forecast. Easy questions suit anyone who has read a thermometer; the expert tier is for metrologists. Every answer was checked against Wikipedia's articles on the scales and their inventors, and the supporting sentence is attached to each question.
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Q 01The Celsius scale is named after an astronomer of which nationality?
Swedish
Anders Celsius (1701–1744) proposed the first version in 1742.
Q 02In Anders Celsius's original 1742 scale, what temperature was 0 degrees?
The boiling point of water
He put freezing at 100; the scale was reversed within two years of his proposal.
Q 03Which French physicist of Lyon inverted Celsius's scale in 1743 to put freezing at 0 and boiling at 100?
Jean-Pierre Christin
He published a mercury 'Thermometer of Lyon' built by the craftsman Pierre Casati that used the modern direction.
Q 04Which botanist reversed the temperature scale in 1744 with a custom greenhouse thermometer?
Carl Linnaeus
His Hortus Upsaliensis of 1745 is the first known Swedish document to report temperatures the modern way up.
Q 05What was the scale commonly called in English before 1948?
Centigrade
From Latin centum, a hundred, and gradus, steps.
Q 06Why did the weights-and-measures authorities rename the scale in 1948?
To honour its inventor and avoid confusion with an angle unit
In French, 'centigrade' also meant one hundredth of a gradian, an angle unit.
Q 07When did BBC Weather finally switch from the old name to 'Celsius'?
February 1985
Australia had gone all-Celsius in its weather reports in September 1972.
Q 08What is absolute zero on the Celsius scale?
−273.15 °C
On the Fahrenheit scale it is −459.67 °F; on the Kelvin scale it is exactly 0 K.
Q 09Which other temperature scale is used within the International System of Units alongside Celsius?
Kelvin
The kelvin is the SI base unit; a degree Celsius has exactly the same size.
Q 10Since 1967, the degree Celsius has been the only SI unit whose full name has what feature?
An uppercase letter
That year 'degrees Kelvin' became simply 'kelvin', with a lower-case k and no degree sign.
Q 11According to the BIPM's rules, how should 30.2 degrees Celsius be written?
30.2 °C, with a space before the unit
The no-space exception applies only to angles: degrees, minutes and seconds of arc.
Q 12Which countries still mainly use Fahrenheit rather than Celsius?
The United States, some island territories and Liberia
Palau, Micronesia, the Marshall Islands and the Cayman Islands are among the holdouts.
Q 13At what temperature do the Celsius and Fahrenheit scales give the same number?
−40
Q 21What temperature was defined as exactly 273.16 K when the absolute unit joined the SI in 1954?
The triple point of water
That is 0.01 °C, the single condition at which ice, liquid water and vapour coexist.
Q 22The 2019 revision of the SI defined the base unit of temperature by fixing which physicist's constant?
Boltzmann's
Every 1 K change now corresponds to exactly 1.380649 × 10⁻²³ joules of thermal energy, decoupling the unit from water entirely.
Q 23Since the scale was decoupled from water, what is water's measured boiling point at one atmosphere?
About 99.97 °C
A one-degree Fahrenheit interval equals five-ninths of a Celsius degree.
Q 14What did Daniel Fahrenheit use to fix the zero of his scale?
A freezing brine of water, ice and ammonium chloride
His upper point was his estimate of human body temperature, first 90 and then 96 degrees.
Q 15How many degrees separate freezing and boiling water on the Fahrenheit scale?
180
Water freezes at 32 °F and boils at 212 °F at standard pressure.
Q 16In which year did Daniel Fahrenheit propose his scale?
1724
He visited England that year and was elected a Fellow of the Royal Society on 5 May.
Q 17Fahrenheit is credited with making the first successful thermometers filled with what?
Mercury
They were more accurate than the spirit-filled instruments then in use, and consistent enough that different observers could compare readings.
Q 18Which Copenhagen astronomer's temperature scale inspired Fahrenheit after they met in 1708?
Ole Rømer
Rømer told him demand for accurate thermometers was high; Fahrenheit was born in Danzig to a German family and worked mostly in the Dutch Republic.
Q 19Who proposed the absolute temperature scale that bears his name in 1848?
Lord Kelvin
Born William Thomson, he derived −273 °C for absolute zero from the expansion coefficient of gases.
Q 20How do you convert a Celsius temperature to the SI absolute scale?
Add 273.15
A change of 1 °C is exactly a change of 1 K, so intervals convert one to one.
On the ITS-90 calibration standard it comes out at roughly 99.974 °C; the melting point of ice is a hair below 0 °C.
Q 24Why is Celsius described as an interval scale rather than a ratio scale?
20 °C is not twice as hot as 10 °C, and 0 is not the bottom
Kelvin, which starts at absolute zero, is a true ratio scale.
Q 25Absolute zero on the Fahrenheit scale is what?
−459.67 °F
The Rankine scale sets its zero there while keeping Fahrenheit-sized degrees.
Q 26Which law of thermodynamics implies that absolute zero cannot be reached in a finite number of steps?
The third
It can be approached but never attained; each further reduction gets harder.
Q 27Which French physicist first raised the question of a lowest possible temperature in 1703?
Guillaume Amontons
He argued that the zero of his instrument would be where the 'spring' of the air vanished.
Q 28The Réaumur scale sets water's boiling temperature at how many degrees?
80
René Antoine Ferchault de Réaumur proposed it in 1730 using a diluted-alcohol thermometer.
Q 29The Rankine scale, proposed in 1859, combines absolute zero with degrees of which size?
Fahrenheit-sized
W. J. M. Rankine was a University of Glasgow engineer; 1 °R equals 5/9 of a kelvin.
Q 30At which university was Anders Celsius professor of astronomy from 1730 until his death?
Uppsala
He founded the Uppsala Astronomical Observatory in 1741 with instruments bought on his European travels.