By what age does birth length usually double?

A) 1 year
B) 2 years
C) 4 years
D) 6 years

Linear growth or height occurs almost entirely as a result of skeletal growth and is considered a stable measurement of general growth. On average, most children have doubled their birth length at age 4 years. One and 2 years are too young for doubling of length. Most children will have achieved the doubling by age 4 years.