Controlling portion size makes a huge difference in weight control and helps you to avoid unwanted extra calories.
The best way to keep portion sizes under control is to weigh and measure your food with food scales, measuring spoons and cups, so you get to know your portion sizes and the calories they contain. Practice until you can 'eyeball' portions of common foods and estimate the calorie content without having to weigh and measure every time.
This is particularly smart when it comes to packaged foods, where the actual weight can be five to ten percent more than the label net weight (the minimum legal weight), and in some cases up to 50 percent more. Manufacturers calculate the calories based on the net weight, which means calories are often under-calculated. For the most accurate calorie count, weigh the product and calculate the extra calories yourself.
If you don't have time to weigh and measure, the American Dietetic Association offers these comparisons as visual guides to portion size: