Clothing comes in standard sizes, but these sizes vary from company to company. While you can always try the shirt on in a brick-and-mortar store, this is not possible when ordering online. Knowing how to measure your shirt size is important, and it can help ensure that you order your shirt in the size. It can also help you if you ever choose to order a custom-sized shirt or ask a tailor to alter one for you.
Keep your body relaxed while taking your measurements.
Do not puff out your chest, suck in your belly, or flex your muscles. If you do any of these, the measurements will not be accurate, and the shirt will not fit. The measuring tape needs to be loose enough to slide around easily. Consider having someone take your measurements for you. This will ensure that your body is straight while you are taking them.
Measure around the widest part of your chest.
Wrap a measuring tape around the widest part of your chest. Keep your body relaxed and do not puff your chest out.
Measure the narrowest part of your waist.
Once again, keep your body relaxed and do not suck your gut in. Wrap the measuring tape around your waist; keep it loose enough so that you can still breathe.