Estimated Fetal Weight Calculator

About this calculator

This calculator implements the Hadlock formula (Hadlock et al., 1985), the most widely used method in obstetric ultrasound for estimating fetal weight from four biometric measurements: biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL), all measured in centimeters. The four-parameter version combines all of these into a single regression equation for log10(EFW), which is generally the most accurate of Hadlock's several published formulas.

Sonographers and obstetricians use this estimated fetal weight (EFW) to track fetal growth trends, screen for growth restriction or macrosomia, and support delivery planning, typically plotting the result on a gestational-age-specific growth percentile chart. Because ultrasound measurement error compounds through the formula, the estimate carries a margin of error of roughly ±10–15% and is always interpreted alongside clinical context by a qualified provider — not as a substitute for medical advice.