Average Weight & Length for a 3-Month-Old Baby

Growth at 3 Months

By 3 months, most babies have gained 50–100% of their birth weight. The average 3-month-old boy weighs about 6.4 kg (14.1 lb) and measures about 62 cm (24.4 in). Girls average about 5.9 kg (12.9 lb) and 60.5 cm (23.8 in). Growth rate is fastest during these early months.

What's Happening at This Age

Three-month-olds are developing rapidly — they can typically lift their head during tummy time, follow objects with their eyes, and may start cooing and smiling socially. Their hands are opening more, and they may bring them to their mouth. Track these alongside growth with our milestone tracker.

Feeding and Growth

Whether breastfed or formula-fed, 3-month-olds typically eat every 3–4 hours. Breastfed babies may grow slightly differently than formula-fed babies in the first year — this is normal and reflected in the WHO growth standards. If you're concerned about feeding or growth, your pediatrician can evaluate your baby's overall pattern.

Tracking Growth Over Time

Remember that a single measurement is less important than the trend. A baby consistently at the 20th percentile is growing normally — just as a baby at the 80th percentile is. Concerns arise when percentiles shift dramatically. Use our growth velocity calculator to measure rate of change between visits.