By what age does birth length usually double?

• A. 2 years
• B. 3 years
• C. 4 years
• D. 5 years

Answer: (C)

Growth milestones for linear growth: birth length typically doubles by around four years. This is a standard pediatric expectation used on growth charts to assess how a child’s height is developing over time. After infancy, length increases steadily but not as rapidly as in the first year, so reaching about twice the birth length around age four is what clinicians commonly see. For example, a newborn around 50 cm would be about 100 cm tall by age four, though individual variation exists. By age two the length is growing but not yet doubled, by age three it’s close but usually not fully doubled, and by age five the child’s length is well past double and continuing to increase.