Conversions

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Conversions

Celsius to Rømer Converter.

Converts a temperature from degrees Celsius to degrees Rømer (°Rø), a historical temperature scale where 0°C equals 7.5°Rø and 100°C equals 60°Rø.

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How it works

  1. 1

    Enter the temperature in degrees Celsius.

  2. 2

    Multiply the Celsius value by 21/40 (or 0.525).

  3. 3

    Add 7.5 to the result.

  4. 4

    The sum is the temperature in degrees Rømer.

celsius * 21 / 40 + 7.5

Frequently asked questions

What is the Rømer scale?

The Rømer scale, proposed by Ole Rømer in 1701, sets 0°Rø as the freezing point of brine and 60°Rø as the boiling point of water. It is now mostly of historical interest.

How do I convert Rømer back to Celsius?

Use the inverse formula: °C = (°Rø - 7.5) × 40/21. For example, 18°Rø equals (18 - 7.5) × 40/21 = 20°C.

Why is the conversion factor 21/40?

Because the Rømer scale divides the interval between 0°C and 100°C into 52.5 Rømer degrees (60 - 7.5 = 52.5). So 1°C = 52.5/100 = 21/40 °Rø.

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Temperature in Rømer

0°Rø

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How it works

Converts a temperature from degrees Celsius to degrees Rømer (°Rø), a historical temperature scale where 0°C equals 7.5°Rø and 100°C equals 60°Rø.

  1. Enter the temperature in degrees Celsius.
  2. Multiply the Celsius value by 21/40 (or 0.525).
  3. Add 7.5 to the result.
  4. The sum is the temperature in degrees Rømer.

Formulas

The math behind this calculator, written out so you can verify the result.

Celsius to Rømer

°Rø = °C × 21/40 + 7.5

Multiply the Celsius temperature by 21/40 and add 7.5 to shift the zero point.

Example:

Input: °C = 20

Calculation: 20 × 21/40 + 7.5 = 10.5 + 7.5

Result: 18°Rø

Real-world use cases

Where this calculation shows up in everyday life.

Historical temperature studies

Convert old scientific records or literature that use the Rømer scale to modern Celsius values.

Example: Reading a 1700s thermometer marked in Rømer.

Educational demonstrations

Teach students about the evolution of temperature scales and linear conversions.

Example: Comparing Celsius, Fahrenheit, and Rømer on a chart.

Curiosity and trivia

Satisfy curiosity about obscure units and how they relate to everyday temperatures.

Example: Finding out what room temperature is in Rømer.

Tips and common mistakes

Tips

  • Remember that 0°C is 7.5°Rø, not 0°Rø.
  • For quick mental estimates, multiply Celsius by 0.5 and add 7.5.
  • Use the inverse formula to check your conversion.
  • The Rømer scale is linear, so the conversion is straightforward.

Common Mistakes to Avoid

  • Forgetting to add the 7.5 offset.
  • Using 0.5 instead of 0.525 as the multiplier.
  • Confusing Rømer with Réaumur (which uses 80° for boiling).

Assumptions and limitations

  • Use the stated inputs and units.
  • Results are estimates for planning and education.
  • Check measurements and source data before making an important decision.