If you're in the market to buy a new sweatshirt and can't find one you like in the store to try on, you can easily buy a sweatshirt from an online retailer. However, if you can't try it on, how will you know if it will fit? Sweatshirts are cut differently from T-shirts and dress clothes. Your usual size may not provide the best fit for you, especially if you are a woman---sweatshirts often use men's sizes. To measure yourself properly for a sweatshirt, you need a tape measure and a friend.
Check the size chart for the sweatshirt you like. Some websites have a link to the size chart directly from the product page; others have a link at the left side or bottom of the page. The size chart will tell you which parts of your body to measure.
Take off any outer garments, such as sweaters or jackets. Wear only what you plan to wear under your sweatshirt, such as a T-shirt.
Have your friend measure the appropriate parts of your body, such as your chest, sleeve, neck, and shoulders. Measure the chest by wrapping the tape measure around the torso, just under the armpits. If you have large breasts, measure the fullest part of your bust. To measure your shoulders (also called "overarm"), your friend will need to wrap the measuring tape around your shoulders near the top of your shoulder blades at the fullest part of your arm. Determine the right sleeve length by running the tape measure down from the top of your shoulder to your wrist.
Find your measurements in the size chart. You may not fit perfectly into one size; if your neck fits a small size, but your chest needs a medium, go with the larger size for comfort.