it is more correct to compare with the height:
Unit：CM
110=4T ：length=60 bust=58; fits for: 100-110cm height / 4 Years Old

120=5T：length=65 bust=62; fits for: 110-120cm height / 5 Years Old

130=6T：length=70 bust=66; fits for: 120-130cm height / 6 Years Old

140=7T-8T：length=75 bust=70; fits for: 130-140cm height / 7-8 Years Old

150=9T-10T：length=80 bust=74; fits for: 140-150cm height / 9-10 Years Old

160=11T-12T：length=85 bust=78; fits for: 150-160cm height / 11-12 Years Old

170=13T-14T：length=90 bust=82; fits for: 160-170cm height / 13-14 Years Old
Note:
1. There is 2-3% difference according to manual measurement (1 inch = 2.54 cm)
2.All measurements in cm, please note 1cm = 0.3937ch, 1 inch = 2.540cm
3. Please check carefully the figures and order the right size, don't completely depend on the "age advice". It's just for reference.