Convert Delisle to Réaumur
Convert degrees delisle to degrees réaumur instantly. °Ré = 80 − (°De × 8/15) — use the live calculator, the exact formula, a reference-temperature table and worked examples. Also check the Réaumur to Delisle converter for the reverse conversion.
Units explained
Delisle
The degree Delisle (°De) is a famously reversed scale: water boils at 0 °De and freezes at 150 °De, so numbers increase as temperature falls. One degree Delisle corresponds to exactly −2/3 of a kelvin.
Invented by French astronomer Joseph-Nicolas Delisle while directing the observatory in St. Petersburg, Russia; his thermometers were originally graduated by the contraction of mercury cooling down from the boiling point of water.
Widely used in 18th-century Russia for about a century. Today it appears only in the history of thermometry, where it is the textbook example of an inverted temperature scale.
Created by Joseph-Nicolas Delisle in St. Petersburg in 1732; recalibrated to the familiar 150-division form by Josias Weitbrecht in 1738.
Réaumur
The degree Réaumur (°Ré) sets the freezing point of water at 0 °Ré and the boiling point at 80 °Ré, so one degree Réaumur equals exactly 1.25 kelvins (5/4 K).
Devised by French scientist René Antoine Ferchault de Réaumur using alcohol thermometers whose working liquid expanded 80 parts per thousand between the freezing and boiling points of water — the origin of the 80-degree span.
Once dominant across 18th- and 19th-century Europe, especially France, Germany, and Russia. It survives today mainly in traditional cheese-making — Parmigiano-Reggiano and Swiss alpine dairies still specify milk temperatures in °Ré.
Introduced by Réaumur in Paris in 1730; it faded from general use after France adopted the Celsius scale with the metric system in the 1790s.
Delisle to Réaumur conversion formula
The exact relationship between degrees delisle and degrees réaumur:
To convert degrees delisle to degrees réaumur, multiply the value by 8/15 and subtract the result from 80. To reverse, multiply the value by 15/8 and subtract the result from 150.
Reference anchors: water freezes at 150 °De = 0 °Ré and boils at 0 °De = 80 °Ré (at standard atmospheric pressure).
How to use this converter
Type a value into the calculator. The result in degrees réaumur updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Réaumur to Delisle converter for the reverse direction.
Step-by-step: convert degrees delisle to degrees réaumur
- Write down the temperature in degrees delisle (°De).
- Multiply the value by 8/15 and subtract the result from 80.
- The result is the same temperature expressed in degrees réaumur (°Ré).
- To reverse, multiply the value by 15/8 and subtract the result from 150 — or open the Réaumur to Delisle converter.
Worked examples
Example 1 — Convert 94.5 °De to °Ré (human body temperature):
80 − (94.5 × 8/15) = 29.6 °Ré
Example 2 — Convert 0 °De to °Ré (the boiling point of water):
80 − (0 × 8/15) = 80 °Ré
Delisle to Réaumur conversion table
Physically meaningful reference temperatures, from absolute zero to the surface of the Sun, converted from degrees delisle to degrees réaumur:
| Delisle [°De] | Réaumur [°Ré] | Reference point |
|---|---|---|
| 559.725 | -218.52 | Absolute zero |
| 210 | -32 | Where Celsius and Fahrenheit coincide (−40°) |
| 176.6666666667 | -14.2222222222 | Zero Fahrenheit (0 °F) |
| 150 | 0 | Water freezes (0 °C / 32 °F) |
| 149.985 | 0.008 | Triple point of water |
| 135 | 8 | Cool day (10 °C / 50 °F) |
| 120 | 16 | Room temperature (20 °C / 68 °F) |
| 112.5 | 20 | Standard laboratory temperature (25 °C) |
| 105 | 24 | Hot day (30 °C / 86 °F) |
| 94.5 | 29.6 | Human body temperature (37 °C / 98.6 °F) |
| 90 | 32 | Heat-wave day (40 °C / 104 °F) |
| 75 | 40 | Hot tap water (50 °C / 122 °F) |
| 0 | 80 | Water boils (100 °C / 212 °F) |
| -120 | 144 | Moderate baking oven (180 °C / 356 °F) |
| -8107.275 | 4403.88 | Surface of the Sun (≈5,505 °C) |
Frequently asked questions
What is 94.5 °De in °Ré?
How do I convert degrees delisle to degrees réaumur?
How do I convert degrees réaumur back to degrees delisle?
At what temperature do the Delisle and Réaumur scales read the same number?
Can a temperature be below absolute zero?
Popular temperature unit conversions
Convert Delisle to other temperature units
Show all Delisle conversions
Modern Standard Scales (4 units)
Historical Scales (3 units)
Scientific & Fixed-Point (3 units)
Sources & references
Conversion relationship (°Ré = 80 − (°De × 8/15)) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- BIPM — International Temperature Scale of 1990 (ITS-90)
The internationally agreed practical temperature scale, defining fixed points (including the triple point of water at 273.16 K) and interpolation instruments used by national metrology institutes for thermometer calibration worldwide.
- CODATA Internationally Recommended Values of the Fundamental Physical Constants
Committee on Data of the International Science Council; authoritative source for the masses of fundamental particles (electron, proton, neutron) and the atomic mass constant.