Baby size by week
Turn tiny measurements into something you can actually picture.
Direct answer: fetal size changes quickly—from millimetres in early pregnancy to roughly half a metre near 40 weeks. Select a week for an approximate measurement and a memorable everyday comparison.
Food comparisons are a memory aid, not a clinical measurement. Fetal growth has a wide healthy range.
What “average size” really means
There is no single exact size for every baby at a given week. The multinational WHO fetal growth study followed 1,387 low-risk pregnancies across 10 countries and collected 8,203 ultrasound measurement sets. Its results showed a wide physiological range even under favourable conditions.
For clinical context, see the WHO fetal growth chart study and the INTERGROWTH-21st longitudinal fetal growth study. Both use ultrasound measurements and are designed for professional interpretation; our object comparisons are simply a friendly way to visualise scale.
Common questions
How big is my baby this week?
Choose a pregnancy week from 4 to 40 to see a playful object comparison plus an approximate length and weight. These are population-level reference values, not a prediction of one baby's exact size.
Why do pregnancy apps compare babies with fruit?
Everyday objects make rapid growth easier to picture. The comparison itself is illustrative; clinicians assess growth using ultrasound measurements and validated growth charts, not fruit or vegetable sizes.
Why is early length measured differently?
Early fetal length is commonly described from crown to rump because curled legs are difficult to measure consistently. Later comparisons often use approximate head-to-heel length.
Can this tool tell whether my baby is growing normally?
No. A qualified clinician interprets ultrasound measurements, gestational age, growth pattern and your individual circumstances. Do not compare a scan report directly with this playful guide.
Not sure of your week? Use the pregnancy week calculator, or explore all free family tools.