Pregnancy & Fertility
Fetal Growth Calculator
Ultrasound numbers meet population charts: estimate fetal weight with the Hadlock formula and see the growth percentile.
Fetal weight percentile compares an ultrasound’s estimated fetal weight with the population average for the same gestational age. The 10th to 90th percentile is typical; below the 10th may indicate growth restriction. Dates are estimates — confirm timing with your provider and ultrasound where relevant.
Hadlock formula: BPD, HC, AC, FL.
Typical: 10th–90th percentile.
Below 10th = possible IUGR, follow up.
Calculate Your Fetal Growth %
Estimated Fetal Weight
What Is Fetal Growth %?
Estimated fetal weight (EFW) combines ultrasound measurements, head, abdomen, and femur, using the Hadlock formula, the standard in obstetric ultrasound.
The percentile places that weight against the population for the same gestational age: 10th–90th is typical. Sustained measurements below the 10th percentile suggest possible growth restriction.
How It Is Calculated
Hadlock: log10(EFW) = 1.3596 − 0.00386·AC·FL + 0.0064·HC + 0.00061·BPD·AC + 0.0424·AC + 0.174·FL
Example: Example: 30 weeks, BPD 78, HC 280, AC 260, FL 58 → EFW ≈ 1,520 g (≈ 45th percentile)
Median EFW by gestational age (Hadlock)
| Week | Median weight |
|---|---|
| 20 | 331 g |
| 24 | 670 g |
| 28 | 1,210 g |
| 32 | 1,953 g |
| 36 | 2,813 g |
| 40 | 3,619 g |
Limitations
- This is an educational estimate, clinical ultrasound software uses full reference curves.
- Measurement error of ±10–15% is inherent to ultrasound biometry.
- Percentile charts vary by population; your unit's chart may differ.
- Diagnoses (IUGR/SGA/LGA) are clinical decisions.
Sources & Review
References used for this calculator’s formulas and thresholds:
Fetal Growth % FAQ
What percentile is normal for fetal weight?
10th–90th percentile is typical. Below 10th suggests possible growth restriction; above 90th suggests a large baby.
What do BPD, HC, AC, and FL mean?
Biparietal diameter, head circumference, abdominal circumference, and femur length, the four standard ultrasound measurements.
How accurate is estimated fetal weight?
Within about ±10–15% of birth weight, accurate enough to guide care, imprecise enough to avoid overreacting to single scans.
What if the baby measures small?
Providers repeat scans to check the growth trend and assess placental blood flow before diagnosing growth restriction.
Important disclaimer: Results are educational estimates, not a substitute for professional medical advice. Discuss your numbers with a clinician before acting on them.