# Celsius to Rømer (°C to °Rø)

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

To convert Celsius to Rømer, multiply by 21/40 and add 7.5. The Rømer scale, devised by Danish astronomer Ole Rømer around 1701, sets the freezing point of water at 7.5°Rø and boiling at 60°Rø. It is historically significant as the direct ancestor of the Fahrenheit scale.

## Formula

°Rø = °C × 21/40 + 7.5

## Conversion Table

| Celsius (°C) | Rømer (°Rø) |
|---|---|
| -40 °C | -13.5 °Rø |
| -20 °C | -3 °Rø |
| -10 °C | 2.25 °Rø |
| 0 °C | 7.5 °Rø |
| 5 °C | 10.125 °Rø |
| 10 °C | 12.75 °Rø |
| 15 °C | 15.375 °Rø |
| 20 °C | 18 °Rø |
| 25 °C | 20.625 °Rø |
| 30 °C | 23.25 °Rø |
| 36 °C | 26.4 °Rø |
| 37 °C | 26.925 °Rø |
| 40 °C | 28.5 °Rø |
| 50 °C | 33.75 °Rø |
| 60 °C | 39 °Rø |
| 80 °C | 49.5 °Rø |
| 100 °C | 60 °Rø |
| 150 °C | 86.25 °Rø |
| 180 °C | 102 °Rø |
| 200 °C | 112.5 °Rø |
| 220 °C | 123 °Rø |
| 250 °C | 138.75 °Rø |
| 300 °C | 165 °Rø |
| 500 °C | 270 °Rø |
| 1000 °C | 532.5 °Rø |

## 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.

### 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.

## Background

Room temperature of 20°C equals 18°Rø. Body temperature (37°C) is about 26.9°Rø. The young Daniel Gabriel Fahrenheit visited Rømer in 1708 and adopted his approach, multiplying the scale by 4 to eliminate the 7.5° freezing point fraction.

## Good to Know

The Rømer scale is one of the most important 'forgotten' temperature scales in history. Without Rømer's work inspiring Fahrenheit, the US might use a completely different temperature system today.

## FAQ

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

The formula is: °Rø = °C × 21/40 + 7.5. For example, 20°C: 20 × 21/40 + 7.5 = 18°Rø.

### What is 0°C in Rømer?

0°C equals 7.5°Rø. Rømer chose this value because he wanted brine (saltwater ice) to be 0° and boiling water to be a round 60°.

### How is the Rømer scale related to Fahrenheit?

Fahrenheit visited Rømer in 1708 and essentially multiplied Rømer's scale by 4 to get whole numbers. Rømer's 7.5° freezing point became Fahrenheit's 32° (7.5 × 4 = 30, adjusted to 32).

## Non-Frequently Asked Questions

### Is Romer the reason we have Fahrenheit?

Partly. Fahrenheit visited Romer's laboratory in 1708 and was inspired by his temperature measurement work. Fahrenheit then improved on Romer's scale by using mercury instead of alcohol. Romer set 0 at brine freezing and 60 at water boiling. Fahrenheit multiplied by 4 and adjusted. Science builds on science.

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## See Also

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