For onesies and capes, check the chest and shoulder width; for dresses, check the waist and dress length. Kids' costumes need extra room for arms and legs, with a knee-length hem being the safest. For adult costumes, if you plan to layer underneath, going one size up from the size chart is more comfortable.
Costumes and Props
How to choose a costume size
First measure your chest and height, then follow the manufacturer's size chart; size up if you need to layer underneath
Short answer
First measure your chest and height, then follow the manufacturer's size chart; size up if you need to layer underneath