Fetal Weight & Size Calculator
Estimate your baby's current weight, length, and size based on gestational age — with fruit-size comparison and development milestones.
Estimate Baby Size
💡 Development This Week
Enter your gestational age to see development milestones.
📖 Understanding Fetal Measurements
Crown–Rump Length (CRL): Measured from the top of the head to the bottom of the buttocks. Standard in the first trimester and most accurate for dating the pregnancy.
Biparietal Diameter (BPD): The diameter across the baby's skull. Used after 13 weeks to estimate gestational age and monitor head growth.
Head Circumference (HC): The circumference of the baby's head. Helps assess brain development and growth symmetry.
Femur Length (FL): The length of the thigh bone. Used to estimate fetal height and overall skeletal development.
Abdominal Circumference (AC): Measured around the baby's abdomen. Particularly useful for estimating fetal weight.
All values shown are population averages. Individual babies vary significantly. Always discuss ultrasound measurements with your healthcare provider.
How It Works
This calculator estimates your baby’s approximate size and weight at your current gestational week, based on average fetal growth data, and compares it to a familiar object (like a piece of fruit) to help make the number easier to visualize.
Fetal measurements are typically calculated from crown-rump length in early pregnancy, transitioning to crown-heel length (head to toe) once the baby is more curled up and measuring in a straight line becomes less practical, usually from around 20 weeks onward.
These figures represent averages across large populations, so your individual baby may run larger or smaller at any given week and still be entirely healthy. Your provider’s own ultrasound measurements, tracked over multiple visits, are a far more reliable indicator of your baby’s specific growth than this general estimate.
Frequently Asked Questions
How accurate are fetal size estimates?
Ultrasound measurements have an inherent error margin of about 10–15% for fetal weight estimates. Accuracy depends on the quality of the ultrasound, the position of the baby, and the operator’s skill. Late-pregnancy estimates are less precise than early ones.
What if my baby measures smaller or larger than average?
Babies come in all sizes. Being in the 10th–90th percentile is considered normal. If measurements are consistently below the 10th percentile (SGA) or above the 90th percentile (LGA), your doctor will monitor more closely. Many factors influence size, including genetics, nutrition, and maternal health.
When can I first see my baby on ultrasound?
A gestational sac can be seen as early as 4–5 weeks. A fetal pole with a heartbeat is usually visible around 6–7 weeks. The first detailed anatomy scan (mid-pregnancy ultrasound) is typically done between 18–22 weeks.
What measurements are taken at each ultrasound?
First trimester (6–13 weeks): Crown–rump length (CRL) for accurate dating. Second trimester (18–22 weeks): BPD, HC, AC, FL for anatomy assessment and growth. Third trimester: BPD, HC, AC, FL to monitor growth and estimate fetal weight.
Can I predict my baby's birth weight?
A late third-trimester ultrasound can estimate birth weight, but its accuracy decreases as the baby grows. Late-pregnancy estimates can be off by 10–15% (about 300–500 g). The average full-term baby weighs about 3.4 kg (7.5 lbs).
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⚠️ Medical Disclaimer: This calculator provides average estimates based on standardized fetal growth curves. Individual measurements vary. This tool is for educational purposes only and should not replace professional medical advice or actual ultrasound measurements. Always consult your healthcare provider.
