Convert Kelvin to Rømer
Convert kelvins to degrees rømer instantly. °Rø = (K × 21/40) − 135.90375 — use the live calculator, the exact formula, a reference-temperature table and worked examples. Also check the Rømer to Kelvin converter for the reverse conversion.
Units explained
Kelvin
The kelvin (K) is the SI base unit of thermodynamic temperature, defined by fixing the Boltzmann constant k at exactly 1.380649×10⁻²³ J/K. Zero kelvin is absolute zero, the lowest temperature physically possible, and kelvin values are written without a degree sign.
Named for William Thomson, 1st Baron Kelvin, who in 1848 calculated the value of absolute zero (about −273 °C) and proposed an absolute thermodynamic scale. His title comes from the River Kelvin, which flows past the University of Glasgow in Scotland.
The universal temperature unit of science and engineering — physics, chemistry, astronomy, and materials science — and the standard for color temperature in photography, displays, and lighting (a 5600 K daylight bulb).
Proposed by William Thomson (Lord Kelvin) in 1848; adopted as an SI base unit by the 10th CGPM in 1954 and redefined through the fixed Boltzmann constant by the 26th CGPM, effective May 20, 2019.
Rømer
The degree Rømer (°Rø) sets the freezing point of water at 7.5 °Rø and the boiling point at 60 °Rø; one degree Rømer equals exactly 40/21 of a kelvin (about 1.905 K).
Created by Danish astronomer Ole Rømer — famous for making the first quantitative measurement of the speed of light — who set 0 °Rø at the temperature of a salt-ice brine and 60 °Rø at boiling water.
Of historical rather than practical importance: it is remembered as the direct ancestor of the Fahrenheit scale and appears mainly in the history of science and in metrology coursework.
Devised by Ole Rømer in Copenhagen, Denmark, in 1701; Daniel Fahrenheit visited Rømer in 1708 and adapted this scale into his own.
Kelvin to Rømer conversion formula
The exact relationship between kelvins and degrees rømer:
To convert kelvins to degrees rømer, multiply the value by 21/40, then subtract 135.90375. To reverse, multiply the value by 40/21, then add 258.8642857143.
Reference anchors: water freezes at 273.15 K = 7.5 °Rø and boils at 373.15 K = 60 °Rø (at standard atmospheric pressure).
How to use this converter
Type a value into the calculator. The result in degrees rømer updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Rømer to Kelvin converter for the reverse direction.
Step-by-step: convert kelvins to degrees rømer
- Write down the temperature in kelvins (K).
- Multiply the value by 21/40, then subtract 135.90375.
- The result is the same temperature expressed in degrees rømer (°Rø).
- To reverse, multiply the value by 40/21, then add 258.8642857143 — or open the Rømer to Kelvin converter.
Worked examples
Example 1 — Convert 310.15 K to °Rø (human body temperature):
(310.15 × 21/40) − 135.90375 = 26.925 °Rø
Example 2 — Convert 373.15 K to °Rø (the boiling point of water):
(373.15 × 21/40) − 135.90375 = 60 °Rø
Kelvin to Rømer conversion table
Physically meaningful reference temperatures, from absolute zero to the surface of the Sun, converted from kelvins to degrees rømer:
| Kelvin [K] | Rømer [°Rø] | Reference point |
|---|---|---|
| 0 | -135.90375 | Absolute zero |
| 233.15 | -13.5 | Where Celsius and Fahrenheit coincide (−40°) |
| 255.3722222222 | -1.8333333333 | Zero Fahrenheit (0 °F) |
| 273.15 | 7.5 | Water freezes (0 °C / 32 °F) |
| 273.16 | 7.50525 | Triple point of water |
| 283.15 | 12.75 | Cool day (10 °C / 50 °F) |
| 293.15 | 18 | Room temperature (20 °C / 68 °F) |
| 298.15 | 20.625 | Standard laboratory temperature (25 °C) |
| 303.15 | 23.25 | Hot day (30 °C / 86 °F) |
| 310.15 | 26.925 | Human body temperature (37 °C / 98.6 °F) |
| 313.15 | 28.5 | Heat-wave day (40 °C / 104 °F) |
| 323.15 | 33.75 | Hot tap water (50 °C / 122 °F) |
| 373.15 | 60 | Water boils (100 °C / 212 °F) |
| 453.15 | 102 | Moderate baking oven (180 °C / 356 °F) |
| 5778 | 2897.54625 | Surface of the Sun (≈5,505 °C) |
Frequently asked questions
What is 310.15 K in °Rø?
How do I convert kelvins to degrees rømer?
How do I convert degrees rømer back to kelvins?
At what temperature do the Kelvin and Rømer scales read the same number?
Can a temperature be below absolute zero?
Popular temperature unit conversions
Convert Kelvin to other temperature units
Show all Kelvin conversions
Modern Standard Scales (3 units)
Historical Scales (4 units)
Scientific & Fixed-Point (3 units)
SI Prefixed Kelvin (5 units)
Sources & references
Conversion relationship (°Rø = (K × 21/40) − 135.90375) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- BIPM — International Temperature Scale of 1990 (ITS-90)
The internationally agreed practical temperature scale, defining fixed points (including the triple point of water at 273.16 K) and interpolation instruments used by national metrology institutes for thermometer calibration worldwide.
- CODATA Internationally Recommended Values of the Fundamental Physical Constants
Committee on Data of the International Science Council; authoritative source for the masses of fundamental particles (electron, proton, neutron) and the atomic mass constant.