Thanks moment,
Thanks lanwater, I’ve been doing this so long I pretty much just look at the door and decide.
This is a fairly light door, 3 probably would have been enough, so 1 more is just enough for a little overkill. But if you ever need to know there is a chart from blum showing their recommendations.

Thanks L/W, I would be embarrassed to show you My desk at the moment, lol
mechanics car doesn’t run, plumbers sinks are back up, …..cabinet makers desk is a door. lol

Figuring out how to do something you have never done is what makes a good challenge.