US clothing sizes are a standardized system used to categorize garments for men, women, and children. Sizes typically range from small (S) to extra-large (XL) for adults, with numerical sizes like 2, 4, 6, and so on for women's clothing. Men's sizes often include chest measurements in inches, such as 38, 40, or 42. Children's sizes are usually designated by age, such as 2T for toddlers or 4 for preschoolers. It's important to note that sizing can vary between brands, so trying on clothing or checking size charts is recommended for the best fit.