it is more correct to compare with the height:
(Unit：CM)
80=9M-12M：Tops length=37 bust=78 sleeve=33 Pants length=46 waist=33 hips=35, fits for: 70-80cm height / 9-12 Months

90=18M-24M：Tops length=37 bust=78 sleeve=37 Pants length=51 waist=35 hips=37, fits for: 80-90cm height / 18-24 Months

100=3T：Tops length=40 bust=81 sleeve=40 Pants length=56 waist=37 hips=38, fits for: 90-100cm height / 3 Years Old

110=4T：Tops length=43 bust=84 sleeve=44 Pants length=62 waist=39 hips=40, fits for: 100-110cm height / 4 Years Old

120=5T：Tops length=46 bust=87 sleeve=47 Pants length=68 waist=41 hips=41, fits for: 110-120cm height / 5 Years Old

130=6T：Tops length=49 bust=90 sleeve=51 Pants length=74 waist=43 hips=43, fits for: 120-125cm height / 6 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.