Measure around the fullest part of the child's chest, keeping tape firmly under his armpits and around his shoulder blades.
Measure around the child's waist, slightly below the natural waist, where he normally wears his pants. Insert your forefinger between the tape and his body to allow ease in fit.
Tip: For the most accurate results, measure yourself in your undergarments.
If your measurements are in between those listed in the size chart, pick the next larger size.