Use your ultrasound’s estimated fetal weight (EFW) and gestational age to see the percentile and a typical range using the published Hadlock 1991 fetal-growth standard.
How to use this calculator
- Enter gestational age: weeks + days from your report (e.g., 28 w 3 d).
- Enter EFW (g): the estimated fetal weight in grams from the same scan.
- Calculate: view the percentile, the typical band, and the ~50th percentile for quick context.
How to read the result
Percentile compares your baby’s weight with peers at the same GA (e.g., 12th means heavier than 12% at that age).
Typical band (~10th–90th) shows a broad “normal” spread for counselling; values can be below/within/above this band.
~50th percentile (median) gives a quick “about average” reference at the selected GA.
Methodology and sources
What this tool calculates
- Percentile for an entered estimated fetal weight (EFW) at a given gestational age (GA).
- A typical weight band at that GA for context.
Inputs and assumptions
- GA is entered in weeks and days. The published equation is used here from 14–40 weeks; values outside that range are not calculated.
- EFW is the ultrasound-reported estimate in grams. The percentile standard is separate from the formula your ultrasound machine used to estimate fetal weight.
- The gestational-age median comes directly from Hadlock’s published 1991 log-weight equation.
Computation
- Median at GA: exp(0.578 + 0.332 × GA − 0.00354 × GA²), with GA in weeks.
- Distribution model: the published natural-log standard deviation of 0.12.
- Percentile: z = (ln(EFW) − ln(median)) / σ; percentile = normal CDF(z) × 100.
- Typical band: the 10th–90th percentiles computed from the same published equation and spread.
Scope and limits
- Percentiles depend on the reference population and the EFW method used. Alternative standards (for example, INTERGROWTH-21st) may yield different centiles.
- Clinical interpretation considers the full picture, including serial growth, amniotic fluid, Dopplers, and maternal factors. This tool is for education, not diagnosis.
Source
Last updated: 7 Sep 2026
Support if you have experienced a loss
Reading about miscarriage, stillbirth, or infant loss can be difficult. If you have experienced a loss, you do not have to use this calculator or read the statistics. You may find it more helpful to talk with your care team or a support organization.
In the United States, groups such as:
offer information and bereavement support. If you are elsewhere, your local health service or a pregnancy and baby loss charity may be able to guide you to support in your region.