it is more correct to compare with the height:(UnitCM)59=0-3Mfull length=54 bust=60 sleeve=22, fits for: 55-59cm height / 0-3 Months66=3-6Mfull length=58 bust=64 sleeve=24, fits for: 59-66cm height / 3-6 Months73=6-9Mfull length=62 bust=68 sleeve=26, fits for: 66-73cm height / 6-9 Months80=9-12Mfull length=66 bust=72 sleeve=28, fits for: 70-80cm height / 9-12 Months90=12-18Mfull length=70 bust=76 sleeve=30, fits for: 80-85cm height / 12-18 MonthsNote:1.There is 2-3% difference according to manual measurement.(1 inch = 2.54 cm)2.All measurement in cm, please note 1cm=0.3937ch, 1 inch=2.540cm3.Please check the figures carefully and order the right size, don't completely depend on the " age advice". It's just for reference.