it is more correct to compare with the height:
(Unit：CM)
90=2T：fits for: 80-90cm height / 2 Years Old

100=3T：fits for: 90-100cm height / 3 Years Old

110=4T：fits for: 100-110cm height / 4 Years Old

120=5T：fits for: 110-120cm height / 5 Years Old

130=6T：fits for: 120-130cm height / 6 Years Old

140=7T：fits for: 130-135cm height / 7 Years Old
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.