Calculate Baby Weight

Calculating baby weight is essential for monitoring fetal development and ensuring a healthy pregnancy. This calculator provides an accurate estimate based on gestational age and other factors. Learn how to use it, understand fetal growth patterns, and discover healthy weight ranges for newborns.

How to Use This Calculator

Using our baby weight calculator is simple and straightforward:

Enter the mother's last menstrual period date or the estimated due date
Select the current date or enter the date of the ultrasound
If available, enter the baby's head circumference measurement
Click "Calculate" to get an estimated baby weight

For most accurate results, use this calculator after the first trimester when fetal growth patterns become more predictable.

Understanding Fetal Growth

Fetal growth follows predictable patterns during pregnancy. The baby's weight increases steadily as the gestational age progresses. Here's a general overview:

First trimester (1-13 weeks): Rapid growth of major organs
Second trimester (14-27 weeks): Growth of muscles and bones
Third trimester (28-40 weeks): Preparation for birth

Average fetal weight formula:

Weight (grams) ≈ (Gestational Age in weeks × 100) + 500

Healthy Weight Ranges

Healthy baby weight ranges vary by gestational age. Here are some general guidelines:

Gestational Age	Average Weight (grams)	Range (grams)
28 weeks	1,000	800-1,200
32 weeks	1,800	1,500-2,100
36 weeks	2,500	2,200-2,800
40 weeks	3,200	2,800-3,600

Consult with your healthcare provider if the baby's weight falls outside these ranges.

Gestational Weeks and Baby Weight

Gestational age is calculated from the first day of the mother's last menstrual period. Here's how it relates to baby weight:

The chart above shows the average baby weight progression throughout pregnancy. Remember that every pregnancy is unique, and these are general guidelines.

Frequently Asked Questions

When should I use this calculator?

This calculator is most accurate after the first trimester when fetal growth patterns become more predictable. For the most precise results, use it after an ultrasound.

What factors affect baby weight?

Baby weight is influenced by gestational age, maternal nutrition, genetics, and overall health. The calculator provides an estimate based on these factors.

What should I do if the baby's weight is outside the normal range?

Consult with your healthcare provider immediately if the baby's weight falls significantly outside the expected range. They can provide guidance and recommend further tests if needed.