The White Guardian

Depends. You can take Kerbin's curve and scale it down, or do things the hard way.

I make an atmosphere nowadays by first coming up with a composition, and then calculating the atmosphere properties: density, molar mass, temperature (using the distance from Kerbol and the guesstimated albedo) and surface pressure. I then create a temperature curve by hand before converting it to polynomials, and then enter all that data into a spreadsheet to create a basic atmosphere model and see what would be a good altitude terminator. Then I just pick a few altitudes and log the pressure data as pressure decreases exponentially with altitude.

This method may sound awfully confusing and overcomplicated but after @OhioBob walked me through it I understand it all and will soon make a video explaining the whole process, which is actually rather straightforward once you know what to do.