Birth Weight Percentile Calculator
Calculate birth weight percentiles based on gestational age using medical standards
Calculate Birth Weight Percentile
Calculator works for gestational ages 22-42 weeks
Weight at birth in grams
Example Calculation
Lucy - Preterm Birth
Gestational Age: 35 weeks, 5 days
Birth Weight: 2500g (5.5 lbs)
Classification: Normal birth weight (NBW)
Result: Approximately 27th percentile
Interpretation: Below average for gestational age but within acceptable range
Michael - Full-term Birth
Gestational Age: 39 weeks, 2 days
Birth Weight: 3200g (7.1 lbs)
Classification: Normal birth weight (NBW)
Result: Approximately 45th percentile
Interpretation: Average range for gestational age
Birth Weight Classifications
ELBW
Extremely Low: < 1000g
VLBW
Very Low: 1000-1500g
LBW
Low: 1500-2500g
NBW
Normal: 2500-4000g
HBW
High: > 4000g
Gestational Age Guide
Preterm
< 37 weeks
Full-term
37-42 weeks
Post-term
≥ 42 weeks
Note: Percentiles are adjusted for gestational age to provide accurate comparisons.
Understanding Birth Weight Percentiles
What Are Birth Weight Percentiles?
Birth weight percentiles compare your baby's weight to other babies of the same gestational age and sex. A baby in the 50th percentile weighs more than 50% of babies born at the same gestational age.
Why Gestational Age Matters
- •Babies grow rapidly in the final weeks of pregnancy
- •Preterm babies naturally weigh less than full-term babies
- •Percentiles adjust for this expected difference
- •Allows for accurate growth assessment regardless of birth timing
Clinical Significance
10th-90th Percentile
Appropriate for gestational age (AGA) - Normal range
< 10th Percentile
Small for gestational age (SGA) - May need extra monitoring
> 90th Percentile
Large for gestational age (LGA) - Monitor for complications
Important: Birth weight is just one factor in neonatal assessment. Healthcare providers consider multiple factors including maternal health, pregnancy complications, and the baby's overall condition.