3-month-old baby weight calculator

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  • weight in the first few days after birth.

  • By two weeks, most healthy babies regain their birth weight.

  • After that, steady growth along the same percentile curve is expected.

Average Baby Weight by Age

Here’s how baby weight typically changes during the first year:

  • At 2 months

    • Boys: ~12 lbs 5 oz (5.6 kg)

    • Girls: ~11 lbs 4 oz (5.1 kg)

    • Babies usually gain about 1 ounce per day in the first three months.

  • At 6 months

    • Boys: ~17 lbs 8 oz (7.9 kg)

    • Girls: ~16 lbs 2 oz (7.3 kg)

    • By six months, most babies have doubled their birth weight.

  • At 12 months

    • Boys: ~21 lbs 3 oz (9.6 kg)

    • Girls: ~19 lbs 10 oz (8.9 kg)

    • By one year, babies typically triple their birth weight.

Understanding the WHO Growth Chart

The WHO growth chart is the gold standard for tracking infant growth worldwide. It’s based primarily on full-term, breastfed babies, though formula-fed infants generally follow a similar growth pattern.

Key points to remember:

  • Growth charts represent averages, not exact targets.

  • The 10th percentile doesn’t mean “failing” — it simply means 10% of healthy babies fall there.

  • What matters is whether your baby grows steadily along their curve.

For example:

  • A baby who has always been near the 15th percentile and continues to grow steadily may be perfectly healthy.

  • A baby who drops from the 50th percentile to the 10th percentile quickly may need closer monitoring.

Should Parents Worry About Percentiles?

Not necessarily. Being on the lower or higher end of the chart does not automatically indicate a problem. Doctors look at the big picture, including:

  • Feeding habits

  • Sleep patterns

  • Developmental milestones

  • Family growth history (some babies are simply genetically smaller or larger)

As Dr. Amin explains:

“Some children fall in lower percentiles but still thrive, meet milestones, and stay healthy. That’s why growth charts are a tool, not the full story.”

Key Takeaways

  • Babies are weighed and measured at birth and throughout their first year.

  • The WHO growth chart helps track healthy growth patterns.

  • Average baby weights:

    • 2 months → ~12 lbs boys / ~11 lbs girls

    • 6 months → double birth weight

    • 12 months → triple birth weight

  • Consistency is more important than being “average.”

  • Sudden percentile changes should be evaluated by a pediatrician.

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