On the Mac there is a wonderful Alfred workflow that converts Px to Rem:
Download direct link:
https://raw.githubusercontent.com/vitorgalvao/requested-alfred-workflows/master/Workflows/Px%20Rem%20Em.alfredworkflow
Simply install, then
- CMD Space: Alfred Bar
- “pxrem” tippen und die Zahl in Pixel angeben. Die Umrechnung in REM wird direkt in die Zwischenablage kopiert.
Many thanks to Vítor Galvão for this great collection of Alfred Workflows