it is more correct to compare with the height:
(Unit：CM)
110=3T/4T：fits for: 95-105cm height / 3-4 Years Old

120=5T：fits for: 105-115cm height / 5 Years Old

130=6T：fits for: 115-125cm height / 6 Years Old

140=7T/8T：fits for: 125-135cm height / 7-8 Years Old

150=9T/10T：fits for: 135-145cm height / 9-10 Years Old

160=11T/12T：fits for: 145-150cm height / 11-12 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.