Q&A for How to Measure Chest Size

Wear whatever a typical undergarment is for you. If you typically wear a certain type of bra, wear that. If you usually go braless, don't wear one. If you're nonbinary and you typically bind, measure your chest while you're wearing your binder.

To measure the chest size of any person, you need to measure the broadest part. To do that, go over the shoulder blades and the widest part of the bust. For men, that's usually directly over the nipples. For women, that will be over the largest part of the bust, wherever that might be.

Chest is a horizontal measurement across the chest at the nipples, it doesn't depend on belly size. Waist is measured at the widest part if you have a convex belly, or at the narrowest point if not. If you are asking about shirt sizing, you will usually have to buy for your biggest measurement.

You could use a piece of yarn or rope as you would the tape measure, mark it off, then use a ruler to get the measurement.

You don't measure around your arms, you lift up your arms and measure around your chest.

The exact sizing will depend on the brand and style of shirt. However, a shirt that measures 36" across the chest would generally fall between an adult small and medium.

Utilize a cloth-reinforced seamstress tape and measure the chest at nipple level. Have them lower their arms and take your reading with a snug tape -- too loose or tight will give you incorrect measurements. Remember, "too big" is easier than "not big enough." You can always take away material, but you can't (easily) add it back.