Baby Size Tracker (by week)
Track fetal size and weight by week of pregnancy with fruit comparisons and development milestones.
Results
Visualization
How It Works
Baby size increases dramatically from a poppy seed at week 4 to about 7-8 lbs at birth. Growth is measured crown-to-rump until week 20, then head-to-heel.
The Formula
Growth follows an exponential curve, with the fastest weight gain in the third trimester (about 0.5 lbs per week from weeks 32-40).
Variables
- CRL — Crown-to-Rump Length — used in first half of pregnancy
- BPD — Biparietal Diameter — head width measurement on ultrasound
Worked Example
At week 20: Baby is about the size of a banana, 6.5 inches long, and weighs about 10.6 oz.
Practical Tips
- Size estimates are averages — healthy babies vary significantly in size.
- Ultrasound weight estimates can be off by 10-15% in either direction.
- Growth rate matters more than absolute size at any single point.
- Fundal height (belly measurement) roughly equals weeks of pregnancy.
- Third trimester is when most weight gain occurs — baby doubles in size.