What Is Reaumur [°r]?
The Reaumur degree, written as °Re or °r, is an old way to measure temperature. It tells how hot or cold something is, like water, air, or metal, but it is not used much today.
Definition
The Reaumur scale is a temperature scale where:
- 0 °Re is the temperature where pure water freezes.
- 80 °Re is the temperature where pure water boils at normal air pressure.
The space between freezing and boiling is divided into 80 equal parts. Each part is one degree Reaumur. So the size of one Reaumur degree is bigger than one Celsius degree.
To compare with Celsius and Fahrenheit:
- 0 °Re = 0 °C = 32 °F
- 80 °Re = 100 °C = 212 °F
History / Origin
The Reaumur scale was created in 1730 by René Antoine Ferchault de Réaumur, a French scientist. He wanted a clear and repeatable way to measure temperature using water as a reference.
In the 1700s and 1800s the scale became popular in parts of Europe, especially in France, Germany, Russia, and Italy. It was used in science, daily life, cooking, and industry.
Over time the Celsius scale replaced Reaumur in most places. Celsius was easier to connect with metric units and became part of the international system used in science and everyday weather reports.
Symbol & Abbreviation
The Reaumur degree is written in a few ways:
- °Re most common modern style
- °Ré older style with accent from the French name Réaumur
- °r short form used in some old texts and tables
In all cases the little circle ° shows degree, and the letter or letters show that the value is on the Reaumur scale, not Celsius or Fahrenheit.
Current Use Around the World
Today the Reaumur scale is mostly a historic unit. It is rarely used in normal life. Celsius is used in almost every country, and Fahrenheit is used in a few countries for weather and home use.
Where Reaumur may still appear:
- Old cookbooks and candy recipes from some European countries.
- Historic weather records and scientific notes.
- Museum tools, such as old thermometers and lab equipment.
- Specialist fields that study history of science or need to read original data.
When people find a value in °Re today they usually convert it to °C or °F.
Example Conversions
Here are the basic formulas to change Reaumur into Celsius and Fahrenheit and back again.
From Reaumur to Celsius
Celsius = Reaumur × 1.25
- 0 °Re = 0 × 1.25 = 0 °C
- 20 °Re = 20 × 1.25 = 25 °C
- 40 °Re = 40 × 1.25 = 50 °C
- 80 °Re = 80 × 1.25 = 100 °C
From Celsius to Reaumur
Reaumur = Celsius × 0.8
- 0 °C = 0 × 0.8 = 0 °Re
- 25 °C = 25 × 0.8 = 20 °Re
- 50 °C = 50 × 0.8 = 40 °Re
- 100 °C = 100 × 0.8 = 80 °Re
From Reaumur to Fahrenheit
First change to Celsius, then to Fahrenheit.
Fahrenheit = (Reaumur × 1.25) × 9 ÷ 5 + 32
- 0 °Re = 0 °C = 32 °F
- 20 °Re = 25 °C = 77 °F
- 40 °Re = 50 °C = 122 °F
- 80 °Re = 100 °C = 212 °F
Related Units
The Reaumur degree is one of several temperature units. Here are the main related units.
- Celsius (°C) Freezing point of water is 0 °C and boiling point is 100 °C at normal pressure. This is the standard scale used in science and most countries.
- Fahrenheit (°F) Freezing point of water is 32 °F and boiling point is 212 °F. Used in daily life in a few countries, such as the United States.
- Kelvin (K) The SI base unit for temperature. Zero kelvin is absolute zero, the coldest possible temperature. Kelvin is used in physics and chemistry. The size of one kelvin is the same as one Celsius degree.
- Rankine (°R) An absolute scale like kelvin but based on Fahrenheit sized degrees. Used in some engineering fields, mostly in the past.
Reaumur connects most closely to Celsius, since both use the freezing and boiling points of water as important marks.
FAQs
What is the Reaumur scale in simple words
The Reaumur scale is an old system for measuring temperature where water freezes at 0 °Re and boils at 80 °Re. It divides that range into 80 equal steps.
Why is the Reaumur degree not used much anymore
The Reaumur scale lost popularity because Celsius fit better with the metric system and became the international standard. Scientists and countries chose Celsius and kelvin for clear global communication.
How do I convert Reaumur to Celsius quickly
To change Reaumur to Celsius, multiply by 1.25. For example, 16 °Re is 16 × 1.25 = 20 °C.
Who invented the Reaumur scale
The Reaumur scale was invented by the French scientist René Antoine Ferchault de Réaumur in 1730.
Is Reaumur the same as Rankine or Kelvin
No, they are different. Reaumur is a relative scale based on water freezing and boiling. Kelvin and Rankine are absolute scales that start at absolute zero, the lowest possible temperature in theory.
Where might I still see temperatures in °Re
You may find °Re in very old cookbooks, historic weather charts, old lab notes, and on antique thermometers in museums or collections.
