Newborn Weight Percentile Calculator

According to the CDC, average birth weight for term newborns (37-42 weeks) is approximately 7.5 lb (3,400 g). Normal birth weight is generally 5 lb 8 oz to 8 lb 13 oz (2,500-4,000 g). Low birth weight (LBW) is below 2,500 g; very low birth weight (VLBW) is below 1,500 g; macrosomia is above 4,000 g.

At 40 weeks gestation, the 50th percentile birth weight is approximately 3,400 g (7.5 lb) for males and 3,300 g (7.3 lb) for females. Values at other gestational ages vary significantly - a baby born at 32 weeks will have a much lower expected weight than one born at 40 weeks.

A birth weight below the 10th percentile for gestational age is called small for gestational age (SGA). This can indicate intrauterine growth restriction (IUGR), which may be caused by placental insufficiency, maternal illness, smoking, or fetal anomalies. SGA babies need close monitoring after birth.

Birth weight above the 90th percentile or above 4,000-4,500 g is called macrosomia or large for gestational age (LGA). Common causes include gestational diabetes, maternal obesity, post-term pregnancy, and fetal genetic conditions. LGA babies have increased risks of shoulder dystocia and birth trauma.

For premature infants, the Fenton growth chart (2013) is widely used as it includes reference data from 22-50 weeks of gestation. The CDC growth charts are designed for children from birth (at 40 weeks) through age 20. Corrected age (gestational age at birth + postnatal age) should be used for preterm infants until 24-36 months.