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Fetal Weight Calculator
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Quickly estimate fetal weight using ultrasound data like Biparietal Diameter (BPD), Abdominal Circumference (AC), and Femur Length (FL). Uses the Hadlock formula to provide a reliable reference for pregnancy assessment.
Only checked Hadlock BPD/AC/FL and BPD/HC/AC/FL formulas remain. All lengths must be centimeters; output grams. Unit guessing, untraced “China guideline”/quick formulas and a fixed ±15% error interval were removed. Error varies by measurement and population. Reference
The length of the widest part between the left and right sides of the fetal head
The circumference of the fetal head
The circumference of the fetal abdomen
The length of the fetal thigh bone
Hadlock four-parameter formula, using biparietal diameter, head circumference, abdominal circumference, and femur length, with higher accuracy.
Enter ultrasound data to start calculation
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
Estimated fetal weight (EFW) is calculated from ultrasound measurements. This calculator applies one of two Hadlock equations and displays whole grams. BPD is fetal head width; HC, head circumference; AC, abdominal circumference; FL, femur length.
Enter every length in centimeters. Each equation produces log10(EFW); the calculator raises 10 to that value and rounds the result to the nearest gram.
Three parameters (BPD, AC, FL)
log10(EFW) = 1.335 − 0.0034 × AC × FL + 0.0316 × BPD + 0.0457 × AC + 0.1623 × FL
Four parameters (BPD, HC, AC, FL)
log10(EFW) = 1.3596 − 0.00386 × AC × FL + 0.0064 × HC + 0.00061 × BPD × AC + 0.0424 × AC + 0.174 × FL
LOINC records the three-input equation as BPD/AC/FL and the four-input equation as AC/BPD/FL/HC.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Three parameters uses BPD, AC, and FL; four also uses HC.
Enter fetal measurements in centimeters. Convert millimeters by dividing by 10 (95 mm = 9.5 cm); fields do not infer units.
Enter positive numbers in each required field to see whole grams. Copy the result beside it; Clear removes values but keeps the equation.
Example (cm): BPD 9.5, HC 33, AC 36.5, FL 7.6 gives 3,816 g (four); BPD 9.5, AC 36.5, FL 7.6 gives 3,923 g (three).
Use cases
See how the tool fits into real work and everyday tasks.
Enter report measurements for an equation-based gram estimate; match the input set to the report method.
Compare equations using the same BPD, AC, and FL; add HC for the four-parameter calculation.
Q&A
Find concise answers to common questions and confusing cases.
They use different variables and coefficients: three uses BPD, AC, and FL; four also uses HC.
No. Convert millimeters to centimeters first by dividing by 10; 95 mm becomes 9.5 cm.
Check that every field required by the selected equation contains a positive number. HC is required only for the four-parameter option.
Notes
Review scope, result limitations, and important precautions before use.
This is equation-based arithmetic, not a medical assessment or a substitute for an ultrasound report or obstetric advice.
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