This size chart is just and indication. Every child is unique. Centimeters will always be centimeters, so just go by how tall your child is and you will be ok.

Length Age
50-56cm New born
56-62cm 1 - 4 months old
68-74cm 5 - 9 months old
80-86cm 10 - 18 months old
92-98cm 1.5 - 3.5 years old
104-110cm 4 - 5 years old 
116-122cm 6 - 7 years old
128-134cm 8 - 9 years old
140-146cm 10 - 11 years old
152-158cm 12 - 13 years old