Please view the shirts sizing chart and read the "how to measure" section for more info.
CHEST: Raise your arms slightly and measure around your body. Be sure to measure across your shoulder blades and the fullest part of your chest.
NECK: Find a collared shirt that fits your neck well. Lay the collar flat on a table and measure the "top" edge of the collar, OR, measure around the base of your own neck, keeping one finger between your neck and the tape measure.
SLEEVE: Place your hand on your hip with your arm bent 90 degrees and measure from the middle of the back of your neck across your shoulder and down your arm to the wrist.