Advanced Fetal Biometry Calculator

Enter fetal measurements

Required fields are BPD, HC, AC, and FL. Optional fields improve interpretation depth but are not mandatory.

BPD (mm) *

HC (mm) *

AC (mm) *

FL (mm) *

OFD (mm)

CRL (mm)

Humerus Length (mm)

Reset

Example data table

BPD (mm)	HC (mm)	AC (mm)	FL (mm)	OFD (mm)	CRL (mm)	Humerus (mm)	Composite GA	Estimated Weight
82	292	284	64	104	—	58	32w 0d	About 2017 g
72	258	240	55	92	—	50	28w 0d	About 1060 g
47	178	151	33	60	—	31	20w 0d	About 346 g

Formula used

1) Gestational age from each measurement
Each biometric value is mapped to gestational age through linear interpolation between internal reference size tables.

2) Composite gestational age
Composite GA = weighted mean of available GA estimates from BPD, HC, AC, FL, CRL, and humerus length.

3) Estimated fetal weight
log10(EFW) = 1.3596 − 0.00386(AC × FL) + 0.0064(HC) + 0.00061(BPD × AC) + 0.0424(AC) + 0.174(FL)
Use BPD, HC, AC, and FL in centimeters. EFW is reported in grams.

4) Cephalic index
Cephalic Index = (BPD ÷ OFD) × 100

5) HC / AC and FL / AC ratios
HC / AC = HC ÷ AC
FL / AC (%) = (FL ÷ AC) × 100

6) Approx percentile
A normalized z-score is calculated from the difference between actual and expected values, then converted into an approximate percentile.

How to use this calculator

Enter the required ultrasound measurements in millimeters.
Add OFD, CRL, or humerus length when available.
Click the calculate button to generate biometric outputs.
Review individual gestational age estimates for each parameter.
Check the composite gestational age and estimated fetal weight.
Study ratios and percentile bands for proportional assessment.
Use the Plotly graph to compare actual and expected sizes.
Download the result card as CSV or PDF when needed.

FAQs

1) What does this calculator estimate?

It estimates gestational age from standard fetal measurements, gives an estimated fetal weight, calculates proportional ratios, and compares entered values with expected reference values.

2) Which measurements are required?

BPD, HC, AC, and FL are required because they drive the core composite gestational age and fetal weight estimate. OFD, CRL, and humerus length add extra detail.

3) Why are CRL and later pregnancy values handled differently?

CRL is mainly useful in earlier pregnancy dating. Later growth assessments rely more on head, abdominal, and long-bone measurements, so CRL is treated as optional supplemental input.

4) Is the estimated fetal weight exact?

No. Estimated fetal weight is a model-based approximation using biometric inputs. It is helpful for trend review, but it is not a direct measured weight.

5) What does the cephalic index show?

It compares biparietal diameter with occipitofrontal diameter. The ratio helps summarize head shape and may support interpretation of head measurement patterns.

6) What do HC/AC and FL/AC ratios tell me?

They help assess proportional growth. HC/AC compares head and abdominal size, while FL/AC compares femur length with abdominal size for an added proportionality check.

7) What does the percentile band mean?

It is an approximate statistical position relative to expected size at the composite gestational age. It helps users see whether a measure trends lower, average, or higher.

8) Can this replace a medical report?

No. It is a supportive educational calculator. Final interpretation should come from a trained clinician who can combine imaging findings, dates, and patient history.