Simple answer

:
meal size = (total calorie load - post workout shake)/(number of other meals)
so at 3000 Calories a day and downing a 600 Cal postworkout shake and aiming for 6 total meals
meal size = 2400/5 = 480 Cal
"Dynamic" answer: In general size your portions according to the amount of activity you expect to do post-meal. Meal = Fuel.
meal 1: more fats allowed
meal 2: portion sized to energy expenditure expected in next 2-4 hrs
preworkout: more carbs allowed
postworkout: more protein allowed, less fat allowed
meal 5: reincorporate fat
presleep: protein/fat or protein/fiber