Newborn Stomach Size Explained: What Your Baby’s Tiny Tummy Can Hold in 2025

Welcome to parenthood, where spit-up, bottles, and diaper changes become your new normal! If you're wondering whether your newborn is eating enough or why they seem to spit up so much, understanding the size of their stomach is key.

Newborns have incredibly small stomachs, which can make feeding feel like a guessing game. To help you navigate this, here’s a clear guide to your baby’s stomach capacity and feeding expectations during the crucial first days and weeks.

Stomach Size vs. Feeding Volume

It's important to differentiate between the physical size of your baby’s stomach and the volume of milk it can comfortably hold. The amount your baby should consume at each feeding depends on this volume, which changes as they grow.

Formula-fed babies might consume larger amounts early on, but this isn’t always ideal. Breastfed babies typically take smaller, more frequent feedings that correspond with their stomach capacity.

Day 1: Pea-Sized Stomach

On the very first day, your newborn’s stomach is about the size of a pea or marble, holding roughly 1 tablespoon of milk per feeding. This explains why colostrum—the nutrient-rich first milk—is produced in small amounts, perfectly suited to your baby’s tiny tummy.

Day 3: Walnut-Sized Capacity

By day three, the stomach grows to about the size of a walnut, accommodating 0.5 to 1 ounce of milk. During this period, mothers often experience breast engorgement as transitional milk replaces colostrum, becoming whiter and more fluid.

Day 10: Golf Ball Size

At around 10 days old, your baby’s stomach reaches the size of a golf ball, comfortably holding 1.5 to 2 ounces per feeding. By this time, your baby should be regaining their birth weight if feeding is going well.

Breastfeeding Insights

Your breasts start producing colostrum as early as 12 to 18 weeks into pregnancy. Even if you don’t plan to breastfeed, colostrum development occurs, so discuss management options with your healthcare provider.

Newborns usually consume about 1 ounce of colostrum in the first 24 hours across multiple feedings. Frequent sucking helps build your milk supply, so if your baby seems constantly hungry, it’s a natural signal for your body to produce more milk.

Newborns also sleep a lot initially, but a good first feed often happens within the first couple of hours after birth.

Between days 2 and 5, colostrum transitions to transitional milk, which is more abundant and resembles whole milk. By 10 to 14 days postpartum, mature milk develops, consisting of foremilk (watery) and hindmilk (rich in fat), adjusting daily to your baby’s needs.

Milk production follows a supply-and-demand principle: the more you empty your breasts, the more milk they produce.

Formula Feeding Tips

When formula feeding, monitor intake carefully to avoid overfeeding, as formula is more filling and the stomach can stretch. Frequent spit-up, fussiness, gassiness, or diarrhea may indicate your baby is consuming too much.

The American Academy of Pediatrics advises against propping bottles to prevent overfeeding. Always hold your baby upright, keep the bottle horizontal, and watch for signs they’re full.

While breastfeeding is recommended exclusively for the first six months by the World Health Organization, supplementing or switching to formula may be necessary in some cases, such as insufficient weight gain or hydration needs.

If returning to work or facing milk supply challenges, consult your doctor for formula options and feeding strategies.

Key Takeaway

Your newborn’s stomach is incredibly small, so frequent, small feedings are normal and expected. If breastfeeding, trust that your baby is unlikely to overeat. Watch for hunger cues, adequate weight gain, and regular wet and dirty diapers to ensure your baby is thriving.

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