Estimated Fetal Weight (Hadlock) Calculator

About this calculator

This calculator applies the Hadlock 4-parameter formula (Hadlock et al., 1985), the most widely used method in obstetric ultrasound for estimating fetal weight. It combines four biometric measurements — biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL), all in centimetres — in a log-linear regression equation built from real birth-weight data.

Adding AC and FL to the simpler formulas that use only head and abdomen measurements is what made the Hadlock formula the clinical standard: it consistently gives one of the lowest error rates among published EFW methods, which is why it's the estimate most sonographers and obstetricians report to expectant parents.