INTERGROWTH-21st newborn size at birth calculator (24 to 42 completed weeks)
Newborn infants, 24 to 42 completed weeks at birth: weight, length, head circumference and weight-to-length ratio at birth.
International standards for size at birth from 33 completed weeks (Villar 2014), and INTERGROWTH-21st's very preterm size at birth references below 33 weeks (Villar 2016).
Z-scores and centiles come from the INTERGROWTH-21st models: a normal distribution below 33 weeks and for the weight-to-length ratio, a skew t distribution from 33 completed weeks.
Tips
- Gestational age at birth: weeks and days, e.g. 33 2/7 (33+2 also works)
- Weight: grams. For kilograms, enter e.g. 1.2kg; for pounds and ounces, e.g. 8-4 for 8 lb 4 oz
- Head circumference and length: cm. For inches, enter e.g. 20"
- The weight-to-length ratio is calculated when both weight and length are entered.