Fetal Growth & Weight Percentile Calculator

Compare your baby's estimated weight against WHO and Hadlock growth charts. See percentile rankings and growth curves for weeks 8-42.

User Rating 0.0 ★★★★★
Total Usage 1 times
Category Womens Health

Leave blank to just see the average range for the selected week.

Is this tool helpful?

Your feedback helps us improve.

★ ★ ★ ★ ★

About

During pregnancy, tracking the baby's growth is essential for monitoring health and development. While every baby is unique, medical professionals use standard "growth curves" to determine if a fetus is Small for Gestational Age (SGA) or Large for Gestational Age (LGA).

This tool utilizes data from the World Health Organization (WHO) and Hadlock's fetal biometry standards to show you where your baby's estimated weight falls compared to the population average. Understanding percentiles can provide reassurance or prompt necessary conversations with your healthcare provider about nutrition, placental health, or due date accuracy.

fetal growth percentiles pregnancy chart

Formulas

The percentile calculation is derived from population distribution curves. The 50th percentile represents the median—exactly average. A baby in the 90th percentile weighs more than 90% of babies at that same gestational age.

Percentile ∝ NormalDist(Weight, μweek, σweek)

Where μ is the mean weight for the week and σ is the standard deviation.

Reference Data

Gestational Week10th Percentile (g)50th Percentile (Average) (g)90th Percentile (g)
20 Weeks255300345
24 Weeks530600670
28 Weeks96011001240
32 Weeks160018002000
36 Weeks240027003000
40 Weeks310035003900

Frequently Asked Questions

If your baby is in the 90th percentile, they are heavier than 90% of babies at that age. If they are in the 10th, they are smaller than 90%. Both can be completely healthy, but extreme outliers (97th) usually require closer monitoring.
Not necessarily. It might simply mean your baby is constitutionally small, perhaps due to genetics (small parents). However, consistently dropping percentiles over time (e.g., from 50th to 10th) is more concerning than staying steady at the 10th.
This calculator compares a *known* or *estimated* weight to averages. It does not measure the baby itself. Ultrasound weight estimates themselves have a margin of error of +/- 15%.
Yes. Maternal nutrition, blood sugar levels (gestational diabetes), and smoking can significantly influence fetal weight. High blood sugar often leads to higher percentiles (macrosomia).