it is more correct to compare with the height:
(Unit: CM)
90=12M-18M：length=37 bust=70 shoulder=26 sleeve=33, fits for: 75-85cm height / 12-18 Months

100=18M-24M：length=39 bust=72 shoulder=27 sleeve=34, fits for: 85-95cm height / 18-24 Months

110=3T：length=42 bust=74 shoulder=28 sleeve=36, fits for: 95-105cm height / 3 Years Old

120=4T：length=45 bust=76 shoulder=29 sleeve=38, fits for: 105-115cm height / 4 Years Old

130=5T：length=48 bust=78 shoulder=30 sleeve=39, fits for: 115-125cm height / 5 Years Old

140=6T-7T：length=51 bust=80 shoulder=31 sleeve=40, fits for: 125-130cm height / 6-7 Years Old
Note:
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=2.540cm
3.Please check the figures carefully and order the right size, don't completely depend on the "age advice". It's just for reference.