The SI unit is just “kelvin” because it’s an absolute scale. Usually “degrees” is only used with Celsius and Fahrenheit scales because they are relative. Not sure about Rankine…
> zero on the Rankine scale is absolute zero, but a temperature difference of one Rankine degree (°R or °Ra) is defined as equal to one Fahrenheit degree
But Rankine is an absolute scale. "By analogy with the SI unit, the kelvin, some authors term the unit Rankine, omitting the degree symbol."
Ah, interesting - this NIST page uses °R, which is at odds with the explanation in the other page on Kelvin (which doesn’t mention Rankine). I’m not sure if that’s because there’s a strong convention to use the degree symbol with Rankine or if there’s an additional reason not mentioned by the Kelvin page
Technically the units of temperature are "degrees Celsius", "degrees Fahrenheit", "Kelvin", etc. ie "degrees" is part of the name of the units "degrees Celsius" and "degrees Fahrenheit". "Kelvin" is the name of the unit by itself, so "degrees" is not supposed to be used before Kelvin.
In practice everyone's so used to saying "degrees" for temperatures that they end up saying it with Kelvin too.
