This chart applies only to costumes manufactured by Pony Express. 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.  
                   
Pony Express - Size Chart - Infant/Toddler              
Size Category Height(Inches) Weight Chest Waist Hips        
Newborn (0-9 Months) 20.5"-28.5" 5.5-19 16"-18" 17"-19" 16.5"-18.5"        
Toddler (1T-2T) 29"-32" 19.5-24 21" 20.5" 21"        
Toddler (2T-4T) 32.5"-41" 24.5-36 23" 21.5" 23"        
                   
Boy's & Girl's Sizes                  
Size Category Height Chest Waist  Hips Back Length Waist to Ankle Inseam    
Small (4-6) 3'3"-3'10" 26" 22.75" 27" 11" 27.25" 20.5"    
Medium (7-10) 3'11"-4'5" 28" 24" 30" 12.5" 31.25" 23.5"    
Large (12-14) (Tween) 4'7"-5' 31" 25.25" 33" 14" 35.25" 26.5"    
                   
Adult/Teen Female                  
Size Category Height Bust Waist  Hips Back Length Inseam      
Teen (2-4) 5'2"-5'4" 33" 25" 35" 16" 26"      
X-Small(2-4) 5'2"-5'4" 33" 25" 35" 16" 26"      
Small(6-8) 5'4"-5'6" 35" 26.5" 37" 16.5" 27.5"      
Medium(10-12) 5'4"-5'7" 37" 28.5" 39" 17" 29"      
Large(14-16) 5'4"-5'8" 39" 30.5" 41" 17.5" 30.5"      
Plus(18-20) 5'4"-5'7" 44"-47.5" 38"-45" 46.5"-50" n/a n/a      
Adult/Teen Males                  
Size Category Height Chest Waist  Neck Inseam        
Small(Teen) 5'6" 36"-38" 30" 15" 30"        
One Size Fits Most 5'8"-6' 42"-44" 40" 16" 33"        
Plus(50-52) 5'8"-6' 50"-52" 46"-48" n/a n/a