Fetal Weight Calculator

Professional fetal weight intelligent estimation tool: supports multiple B-ultrasound parameters including BPD, HC, AC, FL, uses authoritative medical formulas such as Hadlock, Shepard, Campbell, accurately estimates fetal weight EFW, provides growth curve chart, percentile development assessment and personalized pregnancy nutrition advice to help you scientifically manage fetal health and development.

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Fetal Weight Precision Estimation

Enter B-ultrasound measurement data, the system will use authoritative medical formulas to intelligently calculate fetal weight and provide development assessment

weeks
Recommended for use within 14-42 weeks
years
For personalized assessment
Affects assessment standards
B-ultrasound Measurement Data
cm
2.0-10.0cm
cm
7.0-35.0cm
cm
5.0-40.0cm
cm
1.0-8.0cm

cm
Improves accuracy
cm
For head circumference calculation
Sex difference correction
History Comparison
Calculation Time Gestational Age Weight Estimation Percentile Growth Trend Formula Used Action

No history records yet, it is recommended to save each B-ultrasound data for comparison

Weight Change Curve
Tip: The curve visually shows the trend of fetal weight change with gestational age, helping you understand your baby's development.

Fetal Weight Standard Reference Table

Fetal weight percentile standards based on Chinese population data, covering 14-42 gestational weeks

Gestational Week P3(g) P10(g) P25(g) P50(g) P75(g) P90(g) P97(g)
Gestational Week P10(g) P25(g) P50(g) P75(g) P90(g)
Friendly Reminder: Table data is for reference only, individual differences are significant. If fetal weight deviates from the normal range, please consult a professional doctor for further evaluation.

Fetal Weight Calculation Principle Analysis

In-depth understanding of the scientific principles, formula comparison and error analysis of B-ultrasound fetal weight estimation

Common Formulas and Application Scenarios
Formula Name Required Parameters Applicable Weeks Error Range Features
Hadlock AC, FL, BPD/HC 14-42 weeks ±8-15% Most commonly used, high precision
Shepard BPD, AC 20-36 weeks ±10-18% Simple and fast
Campbell HC, AC 16-40 weeks ±12-20% Suitable for abnormal head shape
Factors Affecting Accuracy
  • Fetal position and posture changes
  • B-ultrasound measurement technology and equipment differences
  • Abnormal amniotic fluid volume (too much or too little)
  • Fetal bone development abnormalities
  • Gestational age calculation errors
  • Race and genetic factors
Tips to Improve Accuracy
It is recommended to measure when the fetus is quiet, avoiding false data during fetal movement. The best measurement time is 28-36 weeks of gestation.
Try to provide complete BPD, HC, AC, FL four parameters, which can improve accuracy by more than 30% compared to single parameter estimation.
It is recommended to measure the same parameter 3 times and take the average, which can reduce operational errors and improve result reliability.
B-ultrasound estimation needs to be combined with fundal height, abdominal circumference, maternal weight gain, etc. for comprehensive assessment, and cannot be judged by a single data alone.

About Fetal B-ultrasound, Color Doppler Weight Calculation (Fetal Size Calculator)

What are Biparietal Diameter (BPD), Abdominal Circumference (AC), Femur Length (FL)
The biparietal diameter is not the head circumference, but the length of the parietal bone diameter on both sides of the head near the temples; the abdominal circumference should measure the fetal abdomen in the same plane where the liver and stomach are located; the femur looks like a bone that puppies love to eat on ultrasound, expectant mothers can carefully observe it through the ultrasound display screen.
The occipitofrontal diameter, also known as the "anteroposterior diameter", refers to the longest part of the fetal head from front to back, usually the longest distance from the "nasal root of the forehead" to the "occipital protuberance of the back of the head", so it is called the occipitofrontal diameter.
Fetal head circumference refers to the maximum length around the fetal head. The longest part of the fetal head from front to back is usually the longest distance from the "nasal root of the forehead" to the "occipital protuberance of the back of the head", so the general head circumference is the length around the "nasal root of the forehead" to the "occipital protuberance of the back of the head".
The mother-to-be lies on her back, and the doctor uses a ruler to measure the distance from the mother-to-be's fundus (near the bottom of the sternum) to the upper edge of the pubic symphysis, to estimate the growth of the fetus. When the pregnancy reaches more than 20 weeks, the number of weeks of pregnancy is usually equivalent to this distance.
Some doctors also measure the mother's abdominal circumference: measure the highest part of the abdomen horizontally, but because each mother-to-be's abdominal circumference varies greatly, it is recommended that the mother-to-be regularly measure it at home.
Fetal B-ultrasound Normal Parameter Values

Fetal weight standard table (mean ± standard deviation)

Gestational Week Biparietal Diameter
(Mean)mm		 Abdominal Circumference
(Mean)mm		 Femur Length
(Mean)mm
13 weeks25.2±2.569±16.511.7±3.1
14 weeks28.3±5.777.7±18.213.8±4.8
15 weeks32.3±5.191.3±15.617.4±5.8
16 weeks36.2±5.8103.2±19.221±5.1
17 weeks39.7±4.4114.9±16.225.2±4.4
18 weeks42.5±5.3124.1±027.1±4.6
19 weeks45.2±5.3135.9±2330.3±5
20 weeks48.8±5.8148±033.5±4.7
21 weeks52.2±4.2156.2±18.436.4±4
22 weeks54.5±5.7167±22.338.2±4.7
23 weeks58±4.4179±18.542.1±4.1
24 weeks60.5±5187.4±22.343.6±5.1
25 weeks63.9±7196.4±2246.5±4.2
26 weeks66.8±6.1216.2±2348.7±4.1
27 weeks69.8±5.7218.1±21.251±4.1
28 weeks72.4±6.5228.6±24.153.5±5.5
29 weeks75±6.5237.1±1556.1±4.4
30 weeks78.3±6.2248.8±20.357.7±4.7
31 weeks80.6±6257.8±23.260.3±3.8
32 weeks81.7±6.5262±23.364.3±4.9
33 weeks85±4.7277.8±2365.2±4.6
34 weeks86.1±6.3279.9±25.566.2±4.3
35 weeks87±5.5287.4±28.867.1±4.5
36 weeks88.1±5.7294.4±28.369.5±4.7
37 weeks90±6.3301.4±21.771±5.2
38 weeks90.8±5.9306.3±28.372±4.3
39 weeks92.1±5.9313.4±31.273.4±5.3
40 weeks92.8±5314.9±27.974±5.3
Friendly Reminder: Table data is mean ± standard deviation, individual differences are significant. If parameters deviate from the normal range, please consult a professional doctor for further evaluation.

Authoritative Medical Formula Details

Hadlock Formula - Gold Standard

Formula Expression
Hadlock III (Recommended):
log₁₀(EFW) = 1.335 - 0.0034(AC×FL) + 0.0316(BPD) + 0.0457(AC) + 0.1623(FL)
Hadlock IV:
log₁₀(EFW) = 1.326 - 0.00326(AC×FL) + 0.0107(HC) + 0.0438(AC) + 0.158(FL)
Formula Features
  • Highest precision, error range ±8-15%
  • Applicable to 14-42 gestational weeks
  • Comprehensively considers fetal head, abdomen and femur parameters
  • Widely adopted by medical institutions worldwide
Required Parameters:
Abdominal Circumference (AC) Femur Length (FL) Biparietal Diameter (BPD) or Head Circumference (HC)

Shepard Formula - Classic Simplification

Formula Expression
log₁₀(EFW) = -1.7492 + 0.166(BPD) + 0.046(AC) - 0.0026(AC×BPD)
Formula Features
  • Simple calculation, error range ±10-18%
  • Applicable to 20-36 gestational weeks
  • Only two parameters needed for estimation
  • Suitable for rapid screening
Required Parameters:
Biparietal Diameter (BPD) Abdominal Circumference (AC)

Campbell Formula - Special for Abnormal Head Shape

Formula Expression
ln(EFW) = 4.691 + 1.249(ln(HC)) + 1.089(ln(AC))
Formula Features
  • Suitable for cases with abnormal head shape
  • Error range ±12-20%
  • Applicable to 16-40 gestational weeks
  • High precision requirements for head circumference measurement
Required Parameters:
Head Circumference (HC) Abdominal Circumference (AC)

Comprehensive Formula Comparison Analysis

Formula Name Accuracy Level Error Range Applicable Weeks Required Parameters Optional Parameters Calculation Complexity Clinical Recommendation
Hadlock III ★★★★★ ±8-15% 14-42 weeks AC, FL, BPD HC Medium Strongly Recommended
Hadlock IV ★★★★☆ ±9-16% 14-42 weeks AC, FL, HC BPD Medium Recommended
Shepard ★★★☆☆ ±10-18% 20-36 weeks BPD, AC None Simple Generally Recommended
Campbell ★★☆☆☆ ±12-20% 16-40 weeks HC, AC None Medium Use in Special Cases

Clinical Research and Literature Support

Hadlock Formula Research

Data Source

"Estimation of fetal weight with the use of head, body, and femur measurements--a prospective study."

— Hadlock FP et al., Radiology 1984
Prospective Study n=361 Verified Reliable
Shepard Formula Research

Classic Methodology

"A formula for estimating individual fetal weight using ultrasound measurements."

— Shepard MJ et al., Obstet Gynecol 1982
Classic Formula n=221 Clinical Verification
Campbell Formula Research

Special Case Application

"Estimation of fetal weight by ultrasound measurement of fetal abdominal circumference."

— Campbell S et al., Br J Obstet Gynaecol 1975
Special Application Abnormal Head Shape Professional Recommendation

Why Choose PreMami Fetal Weight Calculator?

Authoritative Medical Formulas

Integrates international authoritative formulas such as Hadlock, Shepard, Campbell, with accuracy up to ±8-15%, clinically verified and reliable

Multi-parameter Intelligent Calculation

Supports multiple B-ultrasound parameters including BPD, HC, AC, FL, HL, improves accuracy by more than 30% compared to single parameter estimation

Percentile Assessment

Based on big data from Chinese population, provides P3-P97 percentile reference, accurately assesses fetal development level

Personalized Nutrition Advice

Intelligently recommends dietary plans based on estimation results, helps scientifically control fetal weight, prevents macrosomia and FGR

Fetal Weight Calculation FAQ

The accuracy of B-ultrasound fetal weight estimation depends on multiple factors. When using the Hadlock formula (AC+FL+BPD), the error range is usually ±8-15%. Under ideal conditions (accurate gestational age, standardized measurement, normal fetal position), the error can be controlled within 10%. However, as the due date approaches, due to relatively fixed fetal position and changes in amniotic fluid volume, the error may increase to 15-20%.

Percentile indicates the position of your baby's weight among fetuses of the same gestational age. For example, P50 means that 50% of fetal weights are below this value, which is a medium level; P10 means that only 10% of fetal weights are lighter, which may indicate a small fetus; P90 means that 90% of fetal weights are lighter, which may indicate a large fetus. Generally, between P10-P90 is considered normal.

The following situations may affect estimation accuracy: 1) Abnormal fetal position (breech, transverse); 2) Abnormal amniotic fluid volume (too much or too little); 3) Thick maternal abdominal wall; 4) Fetal bone development abnormalities; 5) Multiple pregnancies; 6) Gestational age calculation errors; 7) B-ultrasound equipment resolution limitations; 8) Insufficient experience of measurement technicians. In these cases, it is recommended to combine clinical comprehensive assessment.

Fetal weight gain is characterized by stages: 20-28 weeks of gestation gain about 100-150g per week on average; 28-36 weeks is the rapid growth period, gaining 200-250g per week; after 36 weeks, the growth rate slows down, about 150-200g per week. However, individual differences are large, and it is not necessary to pursue "standard values" excessively. What is more important is to observe whether the overall growth trend is normal.

For small fetuses, the cause (placental function, genetics, nutrition, etc.) must first be identified. In terms of nutrition, it is recommended: 1) Increase high-quality protein (fish, lean meat, eggs, milk); 2) Supplement with complex carbohydrates (whole grains, potatoes); 3) Appropriate healthy fats (nuts, deep-sea fish, olive oil); 4) Eat more fresh fruits and vegetables to supplement vitamins; 5) Use maternal nutritional supplements under the guidance of a doctor if necessary. At the same time, ensure adequate rest and avoid overexertion.

The key to controlling diet for large fetuses is to optimize the nutritional structure rather than simply reducing the amount: 1) Reduce intake of refined sugar and sweets; 2) Control fruit intake (200-400g daily), avoid high-sugar fruits; 3) Choose low-GI carbohydrates (brown rice, whole wheat bread); 4) Increase dietary fiber (vegetables, whole grains); 5) Exercise appropriately (walking, prenatal yoga); 6) Monitor blood sugar to rule out gestational diabetes. It is important to carry out under the guidance of a doctor to avoid malnutrition.

In fetal weight estimation, the importance of each parameter is ranked as: Abdominal Circumference (AC) > Femur Length (FL) > Biparietal Diameter (BPD) > Head Circumference (HC). Abdominal circumference best reflects fetal nutritional status and subcutaneous fat thickness, and usually has the largest weight; femur length reflects fetal length; biparietal diameter and head circumference reflect head development. The reason why the Hadlock formula is accurate is that it comprehensively considers these parameters, with AC and FL being the core parameters.

The differences mainly come from: 1) Different calculation formulas used; 2) Differences in B-ultrasound equipment accuracy and measurement technology; 3) Changes in fetal position and amniotic fluid volume during measurement; 4) Different measurement habits and experience of different doctors; 5) Different gestational age calculation methods. It is recommended to conduct serial monitoring under relatively fixed conditions in the same hospital, which is more meaningful for comparison. If the difference is large, you can take the average of multiple measurements as a reference.