Celsius to Réaumur converter

What is the Celsius to Réaumur conversion?

The Celsius to Réaumur converter allows you to easily transform a temperature value expressed in degrees Celsius (°C) into degrees Réaumur (°Ré). The Réaumur scale, less commonly used today, was once a standard temperature measurement in certain European countries, especially in the 18th and 19th centuries. Despite being replaced by the Celsius and Kelvin systems in modern science, the Réaumur scale remains an interesting part of the history of thermometry and occasionally reappears in specific traditional applications, such as European cheese or syrup production.

Understanding how to convert between these two scales is not only useful for historical or practical purposes but also helps understand how different temperature systems relate. Both are metric scales, meaning they divide the range between the freezing and boiling points of water into equal intervals; however, their exact values differ.

Historical insight into the Réaumur scale

The Réaumur scale was introduced in 1730 by the French scientist René Antoine Ferchault de Réaumur. He defined 0 °Ré as the freezing point of water and 80 °Ré as the boiling point of water under standard atmospheric pressure. In contrast, the Celsius scale, later proposed by Anders Celsius in 1742, assigned 0 °C to the freezing point of water and 100 °C to its boiling point.

This difference means the Réaumur scale divides the liquid range of water into 80 equal parts, while Celsius divides it into 100 parts. As a result, each degree Réaumur corresponds to 1.25 degrees Celsius.

Formula

To convert a temperature from Celsius (°C) to Réaumur (°Ré), the following simple linear relationship is used:

$$T_{Ré} = T_{C} \times \frac{4}{5}$$

Where:

• $T_{Ré}$ is the temperature in degrees Réaumur (°Ré)
• $T_{C}$ is the temperature in degrees Celsius (°C)

To convert in the opposite direction, from Réaumur to Celsius, the inverse formula applies:

$$T_{C} = T_{Ré} \times \frac{5}{4}$$

Since both scales share the same zero point (the freezing point of water), there is no need to include an additive term in the formula.

Example calculations

Let’s see some example conversions to grasp how the formula works in practice.

Convert 100 °C to degrees Réaumur.

$$T_{Ré} = 100 \times \frac{4}{5} = 80°Ré$$

So, the boiling point of water at 100 °C is equal to 80 °Ré.

Convert -10 °C to degrees Réaumur.

$$T_{Ré} = (-10) \times \frac{4}{5} = -8°Ré$$

When the temperature is below freezing, the conversion remains linear and consistent across negative values.

If the temperature rises from 15 °C to 30 °C, what is the equivalent change in Réaumur degrees?

$$T_{Ré1} = 15 \times \frac{4}{5} = 12°Ré$$ $$T_{Ré2} = 30 \times \frac{4}{5} = 24°Ré$$

Change = 24°Ré - 12°Ré = 12°Ré

Thus, a temperature change of 15 °C equals a change of 12 °Ré.

Conversion table for common temperatures

The table illustrates that every 5 °C corresponds to 4 °Ré—a steady proportional relationship based on the factor 4/5.

Practical applications

While the Réaumur scale has faded from everyday scientific use, it retains a few niche applications. For instance:

• Cheese production: Some traditional European recipes for cheese, like those from Italy and France, originally specified temperatures using the Réaumur scale.
• Syrup and sugar production: Historic sugar-making documents often reported cooking temperatures in degrees Réaumur.
• Thermometer collections and museums: Collectors and historians often encounter Réaumur-marked thermometers, especially antique European laboratory devices.

Understanding the Réaumur scale is valuable for interpreting historical scientific documents and artifacts.

Notes

1. Both Celsius and Réaumur scales are metric and linear, which means their degree increments correspond directly.
2. The zero points coincide, simplifying conversions.
3. The conversion factor 4/5 = 0.8 shows that the Réaumur degree is larger than the Celsius degree. One degree Réaumur is equivalent to 1.25 degrees Celsius.
4. The Réaumur scale is no longer officially recognized by the SI system, but it preserves its scientific and historical importance.

Frequently Asked Questions

How to convert 60 °C to degrees Réaumur?

Using the formula $T_{Ré} = T_{C} \times \frac{4}{5}$:

$$T_{Ré} = 60 \times \frac{4}{5} = 48°Ré$$

So, 60 °C equals 48 °Ré.

How many degrees Réaumur correspond to a freezing point of 0 °C?

Since both scales start at the same freezing point of water,

$$T_{Ré} = 0 \times \frac{4}{5} = 0°Ré$$

Thus, 0 °C equals 0 °Ré.

Why does water boil at 80 °Ré instead of 100 °Ré?

Because the Réaumur scale divides the range between freezing and boiling points into 80 equal parts instead of 100, as a result, each Réaumur degree is larger and represents 1.25 °C.

How to convert -15 °C to degrees Réaumur?

$$T_{Ré} = (-15) \times \frac{4}{5} = -12°Ré$$

Therefore, -15 °C equals -12 °Ré.

Which scale uses larger degree increments, Celsius or Réaumur?

Réaumur degrees are larger because there are fewer divisions (80 vs. 100) between the freezing and boiling points of water. One degree Réaumur equals 1.25 °C.