Estimated Fetal Weight Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Hadlock 4-parameter formula. Last verified 19 June 2026.

Estimated fetal weight (EFW) is calculated from ultrasound measurements of the baby: biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL). This calculator uses the Hadlock four-parameter equation, one of the most widely used EFW formulas in obstetric ultrasound. Enter the four biometry values in centimetres to estimate fetal weight in grams. This is an information tool and does not replace assessment by a sonographer or clinician.

Biparietal diameter, BPD (cm)

Head circumference, HC (cm)

Abdominal circumference, AC (cm)

Femur length, FL (cm)

Estimated fetal weight (g)

0.00

Estimated fetal weight (lb)

0.00

Hadlock formula

log10(EFW) = 1.3596 - 0.00386*AC*FL + 0.0064*HC + 0.00061*BPD*AC + 0.0424*AC + 0.174*FL
EFW in grams; BPD, HC, AC, FL in centimetres

This is the Hadlock four-parameter (BPD, HC, AC, FL) regression for estimated fetal weight. EFW is the antilog (10 to the power) of the right-hand side.

Worked example

With BPD 8.5, HC 30, AC 28, FL 6.2 cm: log10(EFW) = 1.3596 - 0.00386*28*6.2 + 0.0064*30 + 0.00061*8.5*28 + 0.0424*28 + 0.174*6.2 = 1.3596 - 0.6701 + 0.192 + 0.1452 + 1.1872 + 1.0788 = 3.2927. EFW = 10^3.2927 = approximately 1,962 grams (4.33 lb).

Frequently asked questions

What is estimated fetal weight?

Estimated fetal weight (EFW) is a prediction of the baby's weight derived from ultrasound measurements of the head, abdomen and femur. It helps clinicians monitor growth and plan care, but it is an estimate with a typical margin of error of around 10 to 15 percent.

Why use the Hadlock formula?

The Hadlock four-parameter equation is among the most validated and widely used EFW formulas worldwide. Combining head, abdomen and femur measurements gives a more reliable estimate than any single measurement alone.

Can this replace a clinical scan?

No. This tool reproduces a published formula for information only. Fetal weight estimation should be done by a trained sonographer using calibrated equipment, and any concerns about growth must be discussed with your maternity care provider.

Sources

U.S. National Library of Medicine (PubMed): Hadlock et al. 1985, estimation of fetal weight.

Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.