For best results, measure over your undergarments.
Measure your collar size by taking the tape measure and placing it flush around your neck. To get the most comfortable fit, place two fingers between the tape measure and the neck when measuring.
Measure horizontally across the widest part of the chest/bust. Make sure you keep the tape measure straight across your back.
For men and children, measure horizontally at navel height. For women, measure horizontally across the narrowest part of the waist.