Fetal Weight Percentile
Estimate your baby's weight percentile from ultrasound measurements using the Hadlock formula. Free fetal growth tracker with WHO charts, SGA/LGA classification for India, US, UK.
About This Calculator
The Fetal Weight Percentile Calculator helps expectant parents and healthcare providers estimate a baby's growth during pregnancy using standard ultrasound measurements. By comparing your baby's estimated weight against WHO multinational growth reference data, the calculator determines the weight percentile — a key indicator of healthy fetal development.
Our calculator uses the clinically validated Hadlock formula (Hadlock et al., 1991), which combines four biometric measurements: Abdominal Circumference (AC), Head Circumference (HC), Biparietal Diameter (BPD), and Femur Length (FL). The formula is: log₁₀(EFW) = 1.3596 − 0.00386×AC×FL + 0.0064×HC + 0.00061×BPD×AC + 0.0424×AC + 0.174×FL. The estimated fetal weight is then plotted against the World Health Organization (WHO) fetal growth charts (Kiserud et al., 2017) to determine the percentile.
The result classifies the baby's growth into three categories: SGA (Small for Gestational Age) — below the 10th percentile, indicating the baby is smaller than 90% of peers; AGA (Appropriate for Gestational Age) — between the 10th and 90th percentiles, considered normal; and LGA (Large for Gestational Age) — above the 90th percentile, larger than 90% of peers. The interactive growth chart visualizes where your baby's weight falls among the 10th, 25th, 50th, 75th, and 90th percentile curves.
Regional Notes
India: The WHO growth charts are widely used across Indian hospitals and recommended by the Federation of Obstetric and Gynaecological Societies of India (FOGSI). Indian fetal growth patterns may differ slightly from multinational averages — consider consulting your obstetrician for personalized interpretation.
US: The Hadlock formula and WHO charts are commonly used in American prenatal care. The American College of Obstetricians and Gynecologists (ACOG) recommends routine fetal growth assessment using percentile-based classification for all pregnancies.
UK: The National Institute for Health and Care Excellence (NICE) recommends customised growth charts for UK pregnancies. While our calculator uses WHO multinational reference data, discuss the results with your midwife or obstetrician for the most relevant local interpretation.
Frequently Asked Questions
What is fetal weight percentile?
A fetal weight percentile shows how your baby's estimated weight compares to other fetuses of the same gestational age. For example, a baby in the 50th percentile weighs more than 50% of babies at that same week of pregnancy. It helps doctors assess if the baby is growing appropriately.
How is estimated fetal weight calculated?
Estimated fetal weight (EFW) is calculated using the Hadlock formula: log₁₀(EFW) = 1.3596 − 0.00386×AC×FL + 0.0064×HC + 0.00061×BPD×AC + 0.0424×AC + 0.174×FL, where AC is abdominal circumference, HC is head circumference, BPD is biparietal diameter, and FL is femur length, all in centimeters.
What does SGA and LGA mean?
SGA (Small for Gestational Age) means the baby's weight is below the 10th percentile — over 90% of babies the same age are larger. LGA (Large for Gestational Age) means the baby's weight is above the 90th percentile — only 10% of babies are larger. AGA (Appropriate for Gestational Age) falls between the 10th and 90th percentiles.
What ultrasound measurements are needed?
The calculator requires four standard ultrasound measurements: Abdominal Circumference (AC) around the baby's belly at the liver level, Head Circumference (HC) measured at the thalami plane, Biparietal Diameter (BPD) between the two parietal skull bones, and Femur Length (FL) of the thigh bone. All measurements should be entered in centimeters.
At what gestational age can I use this calculator?
This fetal weight percentile calculator is designed for pregnancies between 14 and 40 weeks of gestation. Earlier pregnancies typically use Crown-Rump Length (CRL) measurements instead. Always consult your healthcare provider for clinical assessment of fetal growth.
Is this calculator accurate for all populations?
The calculator uses the WHO multinational fetal growth charts based on a large longitudinal study across multiple countries, making it applicable globally including India, US, and UK. However, no single growth standard perfectly represents all ethnic groups. Always discuss results with your doctor.
Can I share my calculation results?
Yes! The calculator saves all your input values in the URL, so you can copy the page URL to share your fetal weight calculation with your doctor, partner, or healthcare provider. Simply use the share button to copy the link.