The width of a base or case can be what ever you decide beyond the profile width (in this example 2″). Say, for example, you would like the casing to be 3/4″ x 2-1/2″, so to see what this looks like( the first dashed line) but after seeing the 2-1/2″ width decide you prefer a width of 3-1/4″ (the second dashed line). In both examples the profile width remained the same – 2″ – while the flat area varied in width.

When possible the base will be 1/8″ thinner than the casing to allow for a good fit at doorways. This eliminates a visible line when drywall and iamb don’t match perfectly.