Baby Growth Percentile Calculator
Estimate your baby's weight and length percentile by age and gender using WHO growth charts.
Track milestones from birth to 24 months in lbs or kg.
Baby weight and length growth tracking uses percentile charts from the World Health Organization (WHO) for children birth to age 2, and CDC charts from age 2 onward. These charts establish whether a baby is growing at a healthy rate — both the current measurement and the growth trajectory over time matter.
Weight gain reference rates: Newborn to 3 months: ~1 oz (28g) per day = ~7 oz/week 3–6 months: ~0.7 oz (20g)/day = ~5 oz/week 6–12 months: ~0.5 oz (14g)/day = ~3–4 oz/week 1–2 years: ~0.25 oz (7g)/day ≈ 5 lbs (2.3 kg) per year
Length gain reference rates: 0–3 months: ~1 inch (2.5 cm)/month 3–6 months: ~0.75 inch (2 cm)/month 6–12 months: ~0.5 inch (1.5 cm)/month Year 1 total: approximately 10 inches (25 cm)
Weight-for-length ratio: Weight-for-Length = (Actual Weight ÷ Median Weight at same length) × 100 Below 80% = underweight; above 120% = overweight for length.
Head circumference growth: 0–3 months: ~0.5 inch (1.2 cm)/month Healthy total growth year 1: from ~34 cm at birth to ~46 cm at 12 months
What each variable means:
- WHO vs. CDC — WHO charts reflect children raised in optimal conditions (breastfed, non-smoking home, well-nourished); CDC charts reflect the actual US population; WHO is recommended for birth–24 months internationally
- Percentile vs. absolute value — a consistently 10th-percentile baby who has always tracked there is healthy; a baby who drops from 60th to 20th percentile in 3 months warrants investigation
- Birth weight regain — newborns typically lose 5–10% of birth weight in the first week; expect birth weight to be regained by day 10–14
Reference: average birth measurements:
- Weight at birth: 7.5 lbs (3.4 kg) average; healthy range 5.5–9.5 lbs
- Length at birth: 20 inches (50.8 cm) average; healthy range 18–22 inches
- Head circumference: 13.5 inches (34.3 cm) average
Worked example: Baby girl, 4 months old. Weight: 13.2 lbs (6.0 kg). Length: 24 inches (61 cm).
- WHO chart look-up (4-month girl): 50th percentile weight ≈ 6.4 kg; 50th percentile length ≈ 62 cm
- Weight: 6.0 kg → approximately 35th percentile — normal, slightly below median
- Length: 61 cm → approximately 40th percentile — normal
- Trajectory: If she tracked at 50th percentile at 2 months and is now at 35th, her pediatrician should assess feeding frequency and milk supply. A single percentile drop is common and rarely concerning; ongoing downward crossing warrants evaluation.