On the Catalogues screen you can click the Margin button to show a small margin calculator:
You can enter a start price and margin and it will return the sell price and show the equivalent markup. Or vice versa, if you enter a markup it can show you the equivalent margin.
Click the 
copy buttons next to either margin or markup to copy the figure to the clipboard, to easily paste where you need (which could be the catalogue margin or outside of EQ).
Use the Ctrl + V buttons to paste it in to your chosen destination.