Fetal Weight Percentile Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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Growth and percentile numbers are easiest to understand when the reference method stays visible. Fetal Weight Percentile Calculator converts the entered measurement into the specific percentile estimate supported here.

What this calculator does

Fetal Weight Percentile Calculator uses Sex, Gestational age, Abdominal circumference, Head circumference, Biparietal diameter, and Femur length to calculate Hadlock estimated fetal weight and fetal-weight percentile. Where supported, it also shows WHO fetal-weight percentile, WHO median at gestational age, and Gestational age so the primary result is easier to check. It follows the exact field flow and engine behavior in this plugin rather than describing a different calculator with the same name. Percentiles compare one measurement with a reference population. They describe position in a distribution, not health or diagnosis by themselves, and serial growth or measurement quality often matters more than a single percentile.

How to use it

Enter or select Sex, Gestational age, Abdominal circumference, Head circumference, Biparietal diameter, and Femur length. Use an accurate age or gestational age and a measurement taken with the method expected by the reference chart. If an entry is unknown, do not substitute a guess simply to obtain a number.

How the calculation works

Estimated fetal weight is calculated with a Hadlock ultrasound equation using abdominal circumference, head circumference, biparietal diameter, and femur length. That estimated weight is then compared with the plugin’s WHO fetal-growth reference for the entered gestational age to return a percentile.

Example

Using the sample values prefilled in this calculator, the primary result is 1378.6 g (Estimated fetal weight (Hadlock)), WHO fetal-weight percentile is 20.1%, and WHO median at gestational age is 1,523 g. This example demonstrates the plugin’s own calculation path; replace the sample inputs with verified values before interpreting a real result.

How to interpret the result

A percentile below the 10th or above the 90th can prompt closer obstetric interpretation, but diagnosis of growth restriction or macrosomia requires more than one calculated percentile.

Limitations and notes

Ultrasound estimated fetal weight has meaningful measurement error, especially at extremes. Percentile interpretation should use accurate gestational dating, serial growth, Doppler/clinical context, and the reference standard used by the obstetric service.