Convert Réaumur to Rømer in seconds.

Ever stumbled upon a vintage French recipe requiring temperatures in Réaumur? Or maybe you’re deciphering an 18th-century Danish scientific manuscript filled with Rømer degrees? While these scales aren’t exactly household names today, they offer fascinating glimpses into the history of measurement. Let’s explore how to bridge these two pre-modern temperature systems.

Unit definitions

What is a Réaumur (°Ré)?

Description: Developed by French scientist René Antoine Ferchault de Réaumur in 1730, this scale divided the temperature between freezing and boiling water into 80 equal parts.
Symbol: °Ré
Common uses: Once popular in Europe for scientific and industrial applications, particularly in food production.
Definition: 0°Ré = water freezing point, 80°Ré = water boiling point (at sea level).

What is a Rømer (°Rø)?

Description: Created by Danish astronomer Ole Christensen Rømer in 1701, this was one of the first standardized temperature scales.
Symbol: °Rø
Common uses: Primarily historical, though occasionally referenced in thermodynamics studies.
Definition: 7.5°Rø = brine freezing point, 60°Rø = water boiling point.

Conversion formula

The mathematical relationship between these scales is:
Rømer = (Réaumur × 0.525) + 7.5
To reverse it:
Réaumur = (Rømer − 7.5) ÷ 0.525

Example calculations

1. Converting 20°Ré to Rømer:
   (20 × 0.525) + 7.5 = 10.5 + 7.5 = 18.0°Rø
2. Converting 25°Rø to Réaumur:
   (25 − 7.5) ÷ 0.525 = 17.5 ÷ 0.525 ≈ 33.33°Ré

Conversion tables

Réaumur to Rømer

Rømer to Réaumur

From wine thermometers to modern science

The Réaumur scale’s story begins with its inventor’s fascination with wine fermentation. René de Réaumur originally developed his alcohol-based thermometer for monitoring winemaking processes, never imagining it would become a continental standard. The 80-degree spread between freezing and boiling was chosen for its divisibility (factors include 2, 4, 5, 8, 10, 16, 20, 40), making manual calculations easier in an era before electronic calculators.

Ole Rømer’s contribution came earlier, inspired by his astronomical work. His scale used two fixed points: freezing brine (a common refrigeration method) and boiling water. The 52.5-degree span between these markers created awkward fractions, which might explain why his system didn’t endure as long as Réaumur’s. Interestingly, both scales were eventually supplanted by Celsius’s more intuitive 100 degree system, though the transition took nearly a century in some regions.

Interesting facts

1. Napoleon Bonaparte’s army reportedly used Réaumur thermometers during their Russian campaign.
2. The Rømer scale influenced Fahrenheit’s development of his own temperature system.
3. Some Swiss alpine dairies still use Réaumur for cheese aging traditions.
4. Rømer’s original thermometer contained colored alcohol that expanded dramatically, making it sensitive to minor temperature shifts.
5. At 40°Ré (equal to 50°C), you’d experience water too hot to touch, showing how non-intuitive these scales feel compared to modern standards.

FAQ