Reaumur to Celsius, Fahrenheit & More Converter
Enter a temperature in degrees Reaumur to convert it to Celsius, Fahrenheit, Kelvin, Rankine, Newton, Delisle, and Rømer.
Reaumur Temperature Conversion Tool
Reaumur to Celsius, Fahrenheit & More Formula
Where:
- \(r\) — input temperature in degrees Reaumur (°Re).
- \(C\), \(F\), and \(K\) — temperatures in Celsius (°C), Fahrenheit (°F), and kelvin (K).
- \(R\), \(N\), \(D\), and \(R_{\mathrm{o}}\) — temperatures in Rankine (°R), Newton (°N), Delisle (°De), and Rømer (°Rø).
First convert Reaumur to Celsius, then use the Celsius value to calculate the other scales. The Newton and Rømer divisors shown match the calculator’s formulas; their small decimal approximations have a negligible effect on typical results.
Reaumur to Celsius, Fahrenheit & More – Calculation Example
Example: Convert the default input of 20 °Re to all seven output scales.
First, calculate Celsius:
\[C=20\times1.25=25\ ^\circ\mathrm{C}\]
Then use 25 °C in the remaining formulas:
\[\begin{aligned}F&=25\times1.8+32=77\ ^\circ\mathrm{F}\\K&=25+273.15=298.15\ \mathrm{K}\\R&=25\times1.8+491.67=536.67\ ^\circ\mathrm{R}\\N&\approx25\div3.03030303=8.25\ ^\circ\mathrm{N}\\D&=(100-25)\times1.5=112.5\ ^\circ\mathrm{De}\\R_{\mathrm{o}}&\approx25\div1.9047619+7.5=20.625\ ^\circ\mathrm{R\o}\end{aligned}\]
Result: 20 °Re is 25 °C, 77 °F, 298.15 K, 536.67 °R, approximately 8.25 °N, 112.5 °De, and 20.625 °Rø. The calculator may round displayed values.
How to use the calculator
- Find the field labeled Temperature in Reaumur. It starts at 20 °Re.
- Enter the value you want to convert. You can use a decimal or a negative number; for example, enter 12.5 for 12.5 °Re.
- Read the seven results labeled Celsius, Fahrenheit, Kelvin, Rankine, Newton, Delisle, and Rømer. Each result represents the same temperature on a different scale.
What is the Reaumur temperature scale?
The Reaumur scale is a historical temperature scale found in some European records, scientific writing, and traditional recipes. On this scale, water freezes at 0 °Re and boils at 80 °Re under standard atmospheric pressure. Those same reference points are 0 °C and 100 °C, so each Reaumur degree corresponds to 1.25 Celsius degrees.
That relationship makes Celsius the starting point for every result in this converter. For example, 20 °Re becomes 25 °C, a temperature that can then be expressed as 77 °F. The numbers differ because each scale uses its own degree size, zero point, or both; the physical temperature does not change.
The other outputs can help when comparing sources that use less familiar units. Kelvin and Rankine are absolute temperature scales: their zero is absolute zero, and their units are written K and °R, respectively. Newton, Delisle, and Rømer are historical scales. Delisle runs in the opposite direction from Celsius: its reading falls as temperature rises.
Reference points and practical notes
| Reference point | Reaumur | Celsius | Fahrenheit | Kelvin | Delisle |
|---|---|---|---|---|---|
| Water freezes | 0 °Re | 0 °C | 32 °F | 273.15 K | 150 °De |
| Default example | 20 °Re | 25 °C | 77 °F | 298.15 K | 112.5 °De |
| Water boils at standard atmospheric pressure | 80 °Re | 100 °C | 212 °F | 373.15 K | 0 °De |
These are conversions between temperature readings, not temperature differences. For a change of 1 °Re, the change is 1.25 °C or 2.25 °F; the offsets of 32 °F and 273.15 K do not apply to a temperature change. If you are interpreting an old recipe or instrument reading, also consider whether the source specifies a measurement method or reference conditions.
Water’s boiling temperature varies with atmospheric pressure, so the boiling-point row is a scale reference rather than a promise that water always boils at those readings. The calculator applies its equations to any entered number; values below −218.52 °Re would produce a negative kelvin result and are not physically valid temperatures.
To start with a different unit, use the Celsius converter, Fahrenheit converter, or Kelvin converter. For another historical scale, see the Delisle converter.
Frequently Asked Questions
How do I convert Celsius or Fahrenheit back to Réaumur?
Multiply a Celsius reading by 0.8 to get degrees Réaumur: \(r=0.8C\). For Fahrenheit, first subtract 32, then multiply by \(4/9\): \(r=(F-32)\times4/9\). For example, 68 °F is 20 °C, which is 16 °Re. Keep the Fahrenheit offset when converting a temperature reading, but not when converting a temperature difference.
What is a typical room temperature in degrees Réaumur?
A room at 20–22 °C is about 16–17.6 °Re. There is no single ideal room temperature: comfort depends on clothing, activity, humidity, and personal preference. If an old document gives an indoor temperature in degrees Réaumur, converting it to Celsius can make it easier to judge against modern thermostat settings.
Are °Re, °R, and °Rø the same unit?
No. °Re denotes Réaumur, °R denotes Rankine, and °Rø denotes Rømer. They represent different scales, so the same number followed by each symbol means a different temperature. The abbreviations are easy to confuse, especially in older sources; check the full scale name before entering a reading or comparing results.
Can a Delisle reading be negative for a real temperature?
Yes. A negative Delisle reading does not mean a temperature below absolute zero. Delisle assigns 0 °De to water’s boiling-point reference and decreases as Celsius temperature rises. For example, 120 °C corresponds to −30 °De. The minus sign reflects the direction and zero point of the Delisle scale, not an impossible physical temperature.
Why might another converter give a slightly different Newton or Rømer result?
Converters may use different rounding or intermediate precision. The exact relationships from Celsius are \(N=33C/100\) and \(R_{\mathrm{o}}=21C/40+7.5\). Using rounded decimal factors instead usually changes only the last displayed digits. For practical measurements, the precision of the original reading generally matters more than those tiny calculation differences.
How many decimal places should I use when converting an old Réaumur reading?
Keep only as much precision as the source supports. A historical reading recorded to the nearest whole degree Réaumur does not become more accurate just because a converter displays several decimal places. Preserve extra digits while calculating if needed, then round the final result appropriately. An old instrument’s calibration or reading conditions may introduce more uncertainty than rounding.