Shirts:  Chest. Measure around largest part of chest with measuring tape around shoulder blades and under arms.  Sleeves. Bend elbow and measure from the center back neck, around shoulder, past elbow, to wrist. Note: All long sleeve shirts feature a button tab that allow it to double as a rolled-up short sleeve.  Neck. At the narrow-most part of the neck, measure around the circumference.
Pants:  Waist. Measure around the waistline with a loose tape. Round to the next size up. Note: All waistbands have elastic in rear of pant that provide a flexible, comfortable fit.  Seat. Measured 8" below top of waistband.  Inseam (Voyager Pants). Measured from crotch to leg opening.  Rise. Measured from crotch to top of rear waistband.
Headwear:  Measure circumference across forehead (above brow) above the ears to the back. For all headwear, one size fits all from hat sizes:
6 1/2 (20.5" [or] 52cm) to 7 7/8 (24.625" [or] 63cm)
Select the size range that fits your actual measurements: