Estimated Fetal Weight Calculator (Hadlock)
Estimate fetal weight from ultrasound measurements of biparietal diameter, head circumference, abdominal circumference and femur length using the Hadlock formula. Example: BPD 9.3 cm, HC 33 cm, AC 33 cm and FL 7.2 cm gives about 3,111 g (6 lb 14 oz).
Show steps
How to use the Estimated Fetal Weight Calculator (Hadlock)
- Enter the values in the fields.
- Press Calculate to see the result with the steps shown.
Formula and method
Hadlock (BPD, HC, AC, FL): log10(EFW in g) = 1.3596 – 0.00386 x AC x FL + 0.0064 x HC + 0.00061 x BPD x AC + 0.0424 x AC + 0.174 x FL, with all measurements in cm.
Average fetal weight by week (approximate)
| Weeks | Weight | Length |
|---|---|---|
| 20 | 10.6 oz (300 g) | 10 in |
| 24 | 1.3 lb (600 g) | 11.8 in |
| 28 | 2.2 lb (1.0 kg) | 14.8 in |
| 32 | 3.8 lb (1.7 kg) | 16.7 in |
| 36 | 5.8 lb (2.6 kg) | 18.7 in |
| 40 | 7.6 lb (3.5 kg) | 20 in |
Ultrasound accuracy
Hadlock error is about plus or minus 15% at term. Large and small babies are the hardest to estimate, and measurements of AC have the biggest effect.
What each measurement is
BPD is the head width, HC the head circumference, AC the belly circumference and FL the thigh bone length.
Cautions
This is for learning and for double-checking numbers on a report. This calculator is for education and is not medical advice. Your own doctor, midwife or pediatrician should guide decisions about your care.
Frequently asked questions
How is fetal weight estimated?
From ultrasound measurements of the head, abdomen and femur.
How accurate is it?
Within about 10 to 15%.
What is a normal birth weight?
Typically 5.5 to 8.8 lb (2.5 to 4.0 kg).
Can I measure these at home?
No.
What is macrosomia?
A birth weight over 8 lb 13 oz to 9 lb 15 oz depending on definition.
Does EFW decide delivery?
It is one factor among many.
Sources
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