SLEEVE: Measure from the middle of the back of your neck, over your shoulder, over your elbow, ending at your wrist.
WAIST: Measure the smallest point of your waist all the way around.
INSEAM: Measure from your crotch down to the top of your foot. 
 

Men's Regular Fit Size Chart

Size Chest Sleeve Waist
XS 30" - 32" 32" - 32.5" 25.5" - 27.5"
S 34" - 36" 32.5" - 33" 29.5" - 31.5"
M 38" - 40" 33" - 33.5" 33.5" - 35.5"
L 42" - 44" 34" - 34.5" 37.5" - 39.75"
XL 46" - 48" 35" - 35.5" 42.25" - 44.75"
2XL 50" - 52" 35.5" - 36" 47" - 49.25"
3XL 54" - 56" 36.25" - 36.5" 51.5" - 53.75"
4XL 58" - 60" 36.75" - 37" 56" - 58.25"
5XL 62" - 64" 37.5" 60" - 61.75"
*all measurements done in inches (")