The formula for calculating the height and weight of a small child varies depending on the child’s month and age. The formula for calculating the weight of a small baby from birth to less than 6 months is birth weight + age in months × 0.7. The formula for calculating the weight of a baby from 7 to 12 months is birth weight + age in months × 0.5. The formula for calculating the weight of a toddler from 2 to 12 years is age × 2 + 8. The average monthly growth in height of a small baby from birth to less than 6 months is 2.5cm. The average monthly growth in height of a baby from 7 to 12 months is 1.5cm. The height of 2-12 year olds is age x 5 + 75cm, which means that the child’s height grows about 25cm from birth at the age of 1 week, and 10-12cm from 1 year at the age of 2. From the age of 2 until puberty, the annual height growth is about 6-7cm.