How do I copy formatted formula results in Google Sheets?

I have formula cells outputting numerical results that are then formatted with a " km" (kilometers) postfix. For example, the formula returns 21.4, which is then formatted as 21,4 km. I want to copy and paste the numerical value, so I copy and then on the target cell select "Paste values only". But this assigns the cell with a text value of "21,4 km", and I need the numerical value 21.8 instead. How do I do that?