Here is another helpful visual for estimating portion sizes. This set of photos uses a plate 8.5 inches across (same as the short side of a standard sheet of paper). Go to the article to see LOTS more examples — for fruits, vegetables, meats, and grain-based foods. The article also has tables showing the weights of each of these servings — so you can see that 100 calories of cheddar cheese is packed into 1 ounce, but it takes 5 ounces of cottage cheese to get to 100 calories.
How Should I Use These?
Don’t try to memorize the whole thing! Make a note of portion sizes for the foods you like best, and practice at home when you’re in the kitchen anyway. (And yes, it’s great to have a scale in your kitchen.) Serve out a portion that looks like the right size, and then weigh it to see how close you got. It’s always comically wrong at first, but you’ll get better with experience!