For accurate measurements, get yourself a measuring tape that has both centimetres and inches. You might want to know your size in both units. The best place to start is your neck, measure around the base of your neck, where your shirt collar would normally sit. For comfort, you will want to round up the neck measurement to the nearest whole of half size. For example, if your neck measures 15.3 inches, then you would round that up to 15.5 inches.
Extra tip: we do the 2-finger space between the tape and your neck to ensure space for breathing. The next part of your body you should measure, is your arm length. We suggest you have a friend help you with this part. Stand with your arm slightly bent at your side. Measure from the nape to the wrist. Again, round this up to the nearest whole or half size.