How to choose the size of baby pants

The size of baby pants is mainly based on the age and weight of the baby. Generally speaking:

Newborns (0-1 month) usually choose size 52 pants, which is suitable for babies weighing 2-3.5kg.

2-4 month old babies, if they weigh 3.5-6.9kg, can choose size 59.
3-6 month old babies, weighing 6.9-8.9kg, should choose size 66.
6-9 month old babies, weighing 7.2-9kg, are suitable for size 73 or 75.