👶 Estimated Fetal Weight Calculator
Calculate estimated fetal weight (EFW) using the Hadlock formula from standard ultrasound measurements: biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL). Includes SGA / AGA / LGA classification and fetal weight percentile.
What Is Estimated Fetal Weight (EFW)?
Estimated fetal weight (EFW) is the calculated weight of a fetus before birth, determined from ultrasound measurements. It is one of the most important tools in obstetric care, used to assess fetal growth, detect growth restriction (IUGR) or macrosomia, and guide decisions about delivery timing and mode.
EFW is calculated using formulas that combine several fetal biometric measurements. The most widely used and validated method is the Hadlock formula, developed by Frank P. Hadlock and colleagues in 1984–1985.
The Hadlock Formula
The Hadlock IV formula (also known as Hadlock I in some references) uses four measurements:
log₁₀(EFW) = 1.3596 + 0.0064(HC) + 0.0424(AC) + 0.174(FL) + 0.00061(BPD)(AC) − 0.00386(AC)(FL)
where EFW is in grams and BPD, HC, AC, and FL are in centimeters.
Several variants of the Hadlock formula exist, using different combinations of measurements:
- Hadlock I (IV) — BPD, HC, AC, FL — most accurate when all four measurements are available.
- Hadlock II — AC, FL — used when head measurements are unavailable or unreliable.
- Hadlock III — BPD, AC, FL — a balance between accuracy and measurement availability.
- Hadlock V — BPD, AC — used when femur length cannot be measured.
How to Use This Calculator
Enter the ultrasound measurements in millimeters (mm) as typically reported on ultrasound printouts. The calculator will automatically convert to centimeters for the formula.
- BPD — Biparietal diameter (distance across the fetal skull).
- HC — Head circumference.
- AC — Abdominal circumference.
- FL — Femur length.
- Gestational Age — Current weeks of pregnancy (for percentile classification).
Select the formula variant based on which measurements are available. The Hadlock IV formula (BPD, HC, AC, FL) is recommended when all four are available.
SGA / AGA / LGA Classification
The estimated fetal weight is classified relative to gestational age:
- SGA (Small for Gestational Age) — EFW below the 10th percentile. May indicate intrauterine growth restriction (IUGR) and warrants closer monitoring.
- AGA (Appropriate for Gestational Age) — EFW between the 10th and 90th percentiles. Normal growth.
- LGA (Large for Gestational Age) — EFW above the 90th percentile. May indicate macrosomia, especially in diabetic pregnancies.
Macrosomia is typically defined as birth weight above 4000 g (8 lb 13 oz), with grading: Grade 1 (4000–4499 g), Grade 2 (4500–4999 g), and Grade 3 (>5000 g).
Clinical Applications
- Growth restriction screening: Serial EFW measurements every 2–4 weeks establish growth velocity, which is more meaningful than a single value.
- Macrosomia assessment: EFW above the 90th percentile or above 4000 g prompts delivery planning discussions.
- Delivery planning: ACOG guidelines suggest considering cesarean delivery for EFW above 4500 g in diabetic mothers or 5000 g in non-diabetic mothers.
- Routine anatomy scan: EFW at 18–22 weeks establishes a baseline growth trajectory.
- Preeclampsia monitoring: Serial EFW every 2–3 weeks helps determine optimal delivery timing.
Why Use This Calculator?
- Instant results: Get EFW in grams and pounds/ounces.
- Multiple formulas: Choose from Hadlock I, II, III, or V based on available measurements.
- Percentile classification: Automatic SGA/AGA/LGA classification with visual badge.
- Step-by-step calculation: See exactly how the formula is applied.
- Free & private: No registration, no data storage — all calculations are done in your browser.
❓ Estimated Fetal Weight Calculator FAQ
What is estimated fetal weight (EFW)?
EFW is the calculated weight of a fetus before birth, determined from ultrasound measurements using formulas like the Hadlock equation.
What is the Hadlock formula?
The Hadlock formula is the most widely used method for estimating fetal weight. The Hadlock IV variant uses four measurements: BPD, HC, AC, and FL. It was developed by Frank P. Hadlock in 1985 and remains the clinical standard worldwide.
How accurate is EFW?
EFW has a margin of error of approximately ±15%. This means an EFW of 3000 g could actually be anywhere from about 2550 g to 3450 g. Accuracy is highest when measurements are performed by experienced sonographers and when serial measurements are plotted over time.
What does SGA, AGA, and LGA mean?
SGA (Small for Gestational Age): EFW below the 10th percentile. AGA (Appropriate for Gestational Age): EFW between 10th and 90th percentile. LGA (Large for Gestational Age): EFW above the 90th percentile.
What is macrosomia?
Macrosomia refers to a fetus larger than 4000–4500 grams. It is associated with increased risk of complications during birth, including shoulder dystocia and birth trauma.
Which Hadlock formula should I use?
Use Hadlock IV (BPD, HC, AC, FL) when all four measurements are available — it is the most accurate. Use Hadlock II (AC, FL) when head measurements are unavailable. Your healthcare provider will typically use the formula their ultrasound system is configured for.
Why do I need to enter gestational age?
Gestational age is needed for percentile classification. A 1500 g fetus at 30 weeks is SGA (below 10th percentile), but the same weight at 26 weeks is normal. Without knowing the gestational age, the EFW cannot be properly interpreted.
How are measurements entered?
Enter measurements in millimeters (mm) as typically reported on ultrasound printouts. The calculator automatically converts to centimeters for the Hadlock formula (which requires cm).
Is this calculator a substitute for medical advice?
No. This calculator is for educational and informational purposes only. EFW interpretation requires clinical context, including maternal history, amniotic fluid volume, Doppler studies, and trends over time. Always consult your healthcare provider for medical decisions.
Is this calculator free?
Yes, this calculator is completely free to use. No registration or personal data storage is required.