To find the correct size, we recommend you to combine the two measurements below; the Weight Measurement and the Eye-Chin Distance Measurement.WEIGHT MEASUREMENTThe weight measurement is strongly correlated with the length and size of the face, making it a great measurement for mask sizing.Instructions:1. Use a weight scale to find your weight2. Compare your weight to the table below to find your sizeEYE-CHIN DISTANCE MEASUREMENTThe eye-chin distance measurement is a very accurate method for getting the correct mask size.Instructions:1. Use a ruler and measure the vertical distance between your lower eyelid and your chin2. It can be helpful to do this in front of a mirror or with the help of a friend. It's also helpful to use a book.3. Compare your measurement to the table below to find your recommended size. If you get different recommendations from the 2 methods, follow the one from the Eye-Chin Distance measurement.If your weight or eye-chin distance is on the borderline, pick the bigger one to ensure a better fit.