Your handy guide to portion sizes: Your fist about equals a one-cup serving of milk or raw vegetables. Your thumb about equals one 2-tablespoon serving of peanut butter or salad dressing. Your cupped palm about equals one half-cup serving of cooked fruit, vegetables, beans, or starch. Your thumbnail about equals a one-teaspoon serving of butter or margarine. And your open palm about equals one 3-ounce serving of cooked meat, fish, or poultry.