This chart applies only to costumes manufactured by Franco American Novelties. Each costume on toynk.com lists the manufacturer right below the product title. 
The below size descriptions are provided by the manufacturer.  If you are unsure which size to choose, we suggest buying one size larger.    
                     
Franco American - Size Chart - Child/Teens                  
Size Category Fits Size                  
Toddler 2 to 4                  
Small 4 to 6                  
Medium 8 to 10                  
Large 12 to 14                  
Teen 14 to 16 (same as womens 0-2)                  
Adult Females                    
Size Category Fits Size                  
X-Small  0 to 2                  
Small 4 to 6                  
Medium  8 to 10                  
Large 12 to 14                  
X-Large 16 to 18                  
Plus up to 20                  
Standard up to 12                  
Sexy up to 10                  
Adult Males                    
Size Category Fits Size                  
Standard Up to Jacket 44                  
X-Large Up to Jacket 48