Celsius °C
The original Celsius scale ran backwards: 0 was boiling water and 100 was melting ice. It was flipped round only after his death.
the reference · x °C
General tools
Temperature scales
Eight ways to measure the same thing, laid against one ruler. Convert across all of them, then see how differently they count. Everything runs in your browser - nothing is uploaded.
Side by side
20.0 degrees Celsius
Drag to pan · scroll to zoom · hover or tap to read
How steeply they rise
Celsius across the bottom, and up the side too. Every scale is a straight line, so all that matters is its slope and where it crosses the diagonal.
Hover or tap to read · use the legend to hide a scale
at 25 °C
Where these scales came from
Seven of the eight appeared between 1701 and 1742, in one generation still arguing about which fixed points a thermometer should use at all.
Kelvin K
The only one of the eight with no degrees, just units. Since 2019 it has been defined by the Boltzmann constant rather than by water.
K = °C + 273.15
Fahrenheit °F
Zero is the coldest Fahrenheit could reach with a brine of ice, water, and ammonium chloride. He took the upper fixed point from the human body.
°F = °C × 9/5 + 32
Rankine °R
Kelvin for people who think in Fahrenheit. It is still in everyday use in American thermodynamics and aerospace engineering.
°R = (°C + 273.15) × 9/5
Réaumur °Ré
The European standard for a century. It survives in cheesemaking: milk temperatures for some Italian and Swiss cheeses are still quoted in Réaumur.
°Ré = °C × 4/5
Rømer °Rø
The oldest of the eight and the direct ancestor of Fahrenheit, who visited Rømer and simply refined what he found there.
°Rø = °C × 21/40 + 7.5
Newton °N
Newton had no mercury thermometer, so he measured the expansion of linseed oil. He landed on 33 divisions, an awkward number that buried the scale.
°N = °C × 33/100
Delisle °De
The only one that counts downwards: zero is boiling water and the numbers climb as it gets colder. Russia used it for nearly a century.
°De = (100 − °C) × 3/2
Water is taken to boil at 1013.25 hPa. The colour band is keyed to absolute temperature, not to the zoom level, so the same colour always means the same temperature.
How it works
Eight temperature scales, one shared ruler. The first chart hangs Celsius, Kelvin, Fahrenheit, Rankine, Réaumur, Rømer, Newton, and Delisle side by side against the same physical temperature, so a horizontal line across the page is one temperature read eight different ways. Drag the chart to pan, scroll to zoom, or pick a preset range, and the fixed points - absolute zero, ice melting, water boiling, iron melting - stay pinned where they belong. Hover or tap anywhere on the chart and the converter underneath fills in with that temperature in every scale; type into any one of the eight fields and the other seven follow.
The second chart answers a different question: not what a temperature is called, but how fast each scale counts. Every one of these conversions is affine, value = a × °C + b, so each scale is a straight line plotted against Celsius. The slope is the whole story. Fahrenheit and Rankine climb 1.8 times faster than Celsius because their degree is smaller; Newton is the flattest of the eight because Isaac Newton fitted only 33 divisions between melting ice and boiling water; Delisle is the only line that falls, since it counts upwards as things get colder. Switch to difference mode to subtract the Celsius diagonal and watch the rest fan out.
Example. Type 350 into the Fahrenheit field and the rest of the row resolves at once: 176.7 °C, 449.8 K, 809.7 °R, 141.3 °Ré, 100.3 °Rø, 58.3 °N, and −115 °De. In the slope chart, Delisle crosses the Celsius diagonal at exactly 60 °C - the one temperature where the two scales happen to agree.
FAQ
Which temperature scales are covered?
Eight: Celsius, Kelvin, Fahrenheit, Rankine, Réaumur, Rømer, Newton, and Delisle. Seven of them were invented between 1701 and 1742, by a single generation still arguing about which fixed points a thermometer should use at all.
Why can I not go below −273.15 °C?
That is absolute zero, the point where a system has no thermal energy left to give up. Nothing can be colder, so both charts treat it as a hard wall and the converter clamps any value you type below it.
What does the colour band next to the Celsius axis mean?
It maps absolute temperature to colour: near-black at absolute zero, through blues and greens around habitable temperatures, into orange and white heat. It is tied to the temperature itself, not to the zoom level, so the same colour always means the same temperature.
Are the values I type sent anywhere?
No. All eight conversions and both charts are computed in your browser from simple arithmetic. Nothing you type is uploaded, logged, or stored on a server.