A very basic geometry problem.
Given the info, you're adding 3mm to the cross section circumference of the tire/rim assembly.
Divide by Pi to get roughly a 1mm increase to the diameter, aka width.
Since the inside wheel diameter can't change, the entire 1mm will be added to the height.
This isn't super precise but it's more than close enough for the purpose.
Last edited by FBinNY; 11-18-22 at 10:49 PM.