it is more correct to compare with the height:
100=2T-3T：dress length=55 bust=56 waist=50; fits for: 90-100cm height / 2-3 Years Old

110=4T：dress length=60 bust=60 waist=54; fits for: 100-110cm height / 4 Years Old

120=5T：dress length=65 bust=64 waist=60; fits for: 110-120cm height / 5 Years Old

130=6T：dress length=70 bust=68 waist=64; fits for: 120-130cm height / 6 Years Old

140=7T-8T：dress length=75 bust=72 waist=68; fits for: 130-140cm height / 7-8 Years Old

150=9T-10T：dress length=80 bust=76 waist=72; fits for: 140-150cm height / 9-10 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.