This is a concern, particularly if you're especially large or especially small. Generally, spas approach spa robes  the same way they approach towels: some big and some small. The same applies to the flip-flops and plastic shoes some spas provide. Spas need to cater to a large range of people from tall wide men to teenage girls. Having a one-size-fits-all policy would leave some people uncovered or uncomfortable. Most spas that provide spa robes have an oversized one size fits all robe as their main robe.  However, spas realize that people come in many shapes and sizes and the better spas will carry small robes for petite individual as well as extra large for individuals who may need them.

 If you are concerned about the spa having an appropriate robe for you then you have two options:  The first is to let the spa know when you book the service that you have a special need and give them your robe size.  This way the spa can ensure that you have an appropriate robe and locker for you.    The second is you may always bring your own robe or sandals with you.