Weight based Size Recommendations:
Small 25-50 lbs / 11-22 kg
Medium 51-130 lbs / 23-58 k
Large 130-200+ lbs / 59-90 kg
In general, Large is for most adults. Mediums fit small adult female to about 9 years old. Small fits mask wearer under 50lbs.
Please free feel to contact us if you have more questions regarding which size you should order.