# Celsius to Réaumur (°C to °Ré)

Source: https://www.unitconvertercalculator.com/temperature/celsius-to-reaumur/

To convert Celsius to Réaumur, multiply by 4/5. The Réaumur scale sets water's freezing point at 0°Ré and boiling point at 80°Ré. Once widely used in continental Europe, it is now nearly obsolete, surviving only in a few traditional cheese-making and dairy processes.

## Formula

°Ré = °C × 4/5

## Conversion Table

| Celsius (°C) | Réaumur (°Ré) |
|---|---|
| -40 °C | -32 °Ré |
| -20 °C | -16 °Ré |
| -10 °C | -8 °Ré |
| 0 °C | 0 °Ré |
| 5 °C | 4 °Ré |
| 10 °C | 8 °Ré |
| 15 °C | 12 °Ré |
| 20 °C | 16 °Ré |
| 25 °C | 20 °Ré |
| 30 °C | 24 °Ré |
| 36 °C | 28.8 °Ré |
| 37 °C | 29.6 °Ré |
| 40 °C | 32 °Ré |
| 50 °C | 40 °Ré |
| 60 °C | 48 °Ré |
| 80 °C | 64 °Ré |
| 100 °C | 80 °Ré |
| 150 °C | 120 °Ré |
| 180 °C | 144 °Ré |
| 200 °C | 160 °Ré |
| 220 °C | 176 °Ré |
| 250 °C | 200 °Ré |
| 300 °C | 240 °Ré |
| 500 °C | 400 °Ré |
| 1000 °C | 800 °Ré |

## Units

### Celsius (°C)

A metric temperature scale where 0°C is the freezing point and 100°C is the boiling point of water. Used worldwide except in the US.

### Réaumur (°Ré)

A historical temperature scale where water freezes at 0 °Ré and boils at 80 °Ré. Named after René Antoine Ferchault de Réaumur. Once widely used in Europe.

## Background

Room temperature of 20°C equals 16°Ré. Body temperature (37°C) is 29.6°Ré. Boiling water (100°C) is 80°Ré. The Réaumur scale was the dominant temperature scale in Germany and France during the 18th and 19th centuries before Celsius replaced it.

## Good to Know

The Réaumur scale was used in Germany longer than in France, even though a Frenchman invented it. German meteorological records from the 18th and 19th centuries often require Réaumur-to-Celsius conversion for modern analysis.

## FAQ

### What is the formula for Celsius to Réaumur?

The formula is: °Ré = °C × 4/5. For example, 25°C × 4/5 = 20°Ré. The Réaumur degree is 1.25 times larger than a Celsius degree.

### What is 100°C in Réaumur?

100°C equals exactly 80°Ré. The Réaumur scale has 80 degrees between freezing and boiling, compared to 100 for Celsius.

### Is the Réaumur scale still used anywhere?

The Réaumur scale survives only in niche applications, primarily in traditional cheese-making and dairy processes in parts of Switzerland and Italy. Some old recipes specify curdling temperatures in Réaumur.

## Non-Frequently Asked Questions

### Why does Reaumur have 80 degrees between freezing and boiling?

Reaumur calibrated his thermometer with the expansion of alcohol mixed with water. The 80-degree range was not chosen for mathematical elegance - it was simply what his thermometer showed. Sometimes science is just 'that is what the instrument said.'

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## See Also

- [Réaumur to Celsius](https://www.unitconvertercalculator.com/temperature/reaumur-to-celsius/)