# Rømer to Celsius (°Rø to °C)

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

To convert Rømer to Celsius, subtract 7.5 and multiply by 40/21. Ole Rømer's scale (c. 1701) sets water's freezing point at 7.5°Rø and boiling at 60°Rø. This conversion is needed only for historical thermometry research.

## Formula

°C = (°Rø − 7.5) × 40/21

## Conversion Table

| Rømer (°Rø) | Celsius (°C) |
|---|---|
| -10 °Rø | -33.33333333333 °C |
| 0 °Rø | -14.28571428571 °C |
| 5 °Rø | -4.7619047619 °C |
| 7.5 °Rø | 0 °C |
| 10 °Rø | 4.7619047619 °C |
| 15 °Rø | 14.28571428571 °C |
| 20 °Rø | 23.80952380952 °C |
| 25 °Rø | 33.33333333333 °C |
| 30 °Rø | 42.85714285714 °C |
| 40 °Rø | 61.90476190476 °C |
| 50 °Rø | 80.95238095238 °C |
| 60 °Rø | 100 °C |
| 80 °Rø | 138.09523809524 °C |
| 100 °Rø | 176.19047619048 °C |
| 200 °Rø | 366.66666666667 °C |

## Units

### Rømer (°Rø)

A temperature scale proposed by Ole Christensen Rømer in 1701. Water freezes at 7.5 °Rø and boils at 60 °Rø. It influenced Fahrenheit's scale development.

### 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.

## Background

Rømer body temperature (about 26.9°Rø) equals 37°C. Boiling water at 60°Rø equals 100°C. The Rømer scale's main importance is historical: Fahrenheit visited Rømer in 1708 and adapted his scale to create the Fahrenheit system still used in the US today.

## Good to Know

Rømer's scale is historically fascinating as the direct ancestor of Fahrenheit. The seemingly arbitrary numbers in Fahrenheit (32° freezing, 212° boiling) make much more sense when you realize they are Rømer's numbers multiplied by roughly 4.

## FAQ

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

The formula is: °C = (°Rø − 7.5) × 40/21. For example, 18°Rø: (18 − 7.5) × 40/21 = 10.5 × 1.905 = 20°C.

### What is 7.5°Rø in Celsius?

7.5°Rø equals exactly 0°C - the freezing point of water. Rømer set brine (saltwater) freezing at 0° and pure water freezing at 7.5°.

### What is 60°Rø in Celsius?

60°Rø equals exactly 100°C - the boiling point of water. Rømer chose 60° for boiling as a round, highly divisible number.

## Non-Frequently Asked Questions

### Is Romer related to ancient Rome?

No. Ole Christensen Romer was a Danish astronomer who created his temperature scale around 1701. He is better known for being the first person to measure the speed of light. His temperature scale sets 0 at a brine freezing point and 60 at boiling water. Even geniuses sometimes make forgettable contributions alongside their masterpieces.

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## See Also

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