STEP 1 Measure from the bridge of your nose to the tip of your chin. It may be helpful to have a friend assist you.  Measuring from the height of the bridge of your nose (usually just below your eye line) down to the tip of the chin, and do not measure past the tip of your chin. STEP 2 Match your measurement with the given sizes below to find the correct sizing for you. We offer 3 different sizes of masks Medium, Large, and X-Large. Medium 3.5"-4" Large 4"-4.5" X-Large 4.5"+ If your measurements lie in-between sizes, we recommend using your weight as a secondary reference. Medium up to 140 lbs Large 140 lbs - 200 lbs Extra Large 200 lbs and up Additional sizing information here