Ring slings are measured from the gathered edge on the rings along the shorter of the two long hems as this is the usable length a sling offers. Bijou Wear ring slings are sewn with a floating shoulder, which provides padding without being padded and good spreadability. They can be worn on either your right or left. Check out instructions on wearing a sling here.
They are measured in inches as follows: Small = 70 inches // Medium = 75 inches // Large = 80 inches // Extra Large = 85 inches // Extra Extra Large = 90 inches
A good rule to follow is to buy your t-shirt size, though if you are large busted or have a large ribcage or carry a large toddler, you might choose to size up. However, larger people can wear smaller ring slings and vice versa. The only difference will be the amount of "tail" hanging down from the rings. Remember, they are only five inches different from each other, so don't be wary of getting a shorter or longer size than you might think! You can measure a loop from one shoulder to opposite hip and back with a soft tape to see how long your adjusting tail will be with each of the sizes.
During its first bath your ring sling will shrink slightly, which is normal. We cut the fabric so that it will shrink to the size that you ordered (within tolerances).