I include 2 scoops of ON whey in my pwo shake, a serving of creatine, and 1/4 cup of dextrose. And I mix it with about 15 oz of water. That works out to be 46 grams of protein, 39 grams of carbs, and 3 grams of fat for a total of 389 calories.
Just remember that every tablespoon of dextrose is about 10 grams of carbs, which is 40 calories. I think that 30 to 40 grams is a good amount to include, but it all depends on how intense your workout is and what your diet's
macronutrient breakdown allows for.