The Ultimate Baby Clothes Sizing Guide: Which Brands Run Small?

The first hurdle is understanding what the labels are trying to tell you. Most baby clothes are sized by age (like ‘Newborn’ or ‘3-6 Months’), but here’s the secret: a baby’s weight and length are far more reliable indicators of fit than their age. Just like adults, babies come in all beautiful shapes and sizes! A long, lean 2-month-old might need a ‘3-6 month’ size for length, while a delightfully chunky 2-month-old might need it for width.

Think of the age on the tag as a starting point, not a rule. The real truth is usually in the fine print on the brand’s website or sometimes on the tag itself, where they list weight and height ranges. To give you a general idea, here is a standard sizing chart. Always remember to check the specific chart for the brand you’re buying!

A Nurse’s Tip: Don’t remove the tags from all those gifted outfits at once! Wash a few items in each size range and see how they fit your baby. You might find you skip the ‘Newborn’ size entirely or live in ‘0-3 Months’ for what feels like forever. Every baby’s growth journey is unique.

Alright, this is the moment you’ve been waiting for! Here’s the inside scoop on how some of the most popular baby brands typically fit. I’ve chatted with thousands of parents over the years, and this is the consensus. Use this table as your secret weapon when shopping online or building your registry.

Remember, this is a general guide. Brands can change their manufacturing, and even within a single brand, one style of sleeper might fit differently than another. The best strategy is to know your baby’s current height and weight and use that as your primary guide.

Now that you’re an expert on brand sizing, let’s talk strategy. Here are my tried-and-true tips for making sure your baby is always comfortable and you’re not wasting money on clothes that get worn once.

• Know Your Measurements: Keep a note on your phone with your baby’s current weight and height. When shopping online, always, always look for the brand’s specific size chart and buy based on those numbers, not the age on the label.
• When in Doubt, Size Up: This is the golden rule of baby clothes. They will always grow into it. A little extra room is fine, but clothes that are too tight are uncomfortable and can even be unsafe, especially for sleep.
• The Pre-Wash Test: Baby clothes, especially 100% cotton items, are notorious for shrinking. Before you commit to a brand, buy one piece, wash and dry it, and see how it fits. If it shrinks significantly, you’ll know to size up for future purchases.
• Consider the Diaper: Are you using bulky cloth diapers? You will almost certainly need to size up in pants and onesies to accommodate the extra fluff in the trunk!
• The One-Finger Rule: For a safe and comfortable fit, you should be able to easily slip one finger between the fabric and your baby’s neck, wrists, and ankles. If it’s a struggle, it’s too tight.
• Shop Secondhand to Experiment: A great way to try out different brands without a big investment is to shop at consignment stores or online marketplaces. You can see how different brands fit your baby and find your favorites.
• Keep Receipts and Tags: It’s so tempting to wash everything from your baby shower at once, but resist! Keep tags on and receipts handy. You might receive a dozen ‘Newborn’ outfits only to have a 9-pound baby who goes straight into ‘0-3 Months’.

Sizing woes don’t stop at onesies! Other essential items have their own quirks. Here’s a quick rundown on how to navigate them.

Pajamas & Sleepers

This is where fit is a matter of safety, not just comfort. To reduce fire risk, the Consumer Product Safety Commission (CPSC) mandates that baby and children’s sleepwear must be either flame-resistant or snug-fitting. Most of the soft, breathable cotton or bamboo sleepers you love fall into the snug-fitting category. This is why they often look so long and skinny! Don’t be tempted to size up too much for sleepwear. You want it to be close to the body without being constricting.

Socks & Booties

The eternal quest to find a baby sock that actually stays on! Sock sizing is often grouped into larger age ranges (e.g., 0-6 months). Look for socks with good elastic at the ankle but not so tight that it leaves a mark. Brands like Bombas or Zutano booties are often parent-favorites for their ability to stay put.

Outerwear & Layers

For jackets, fleece buntings, and snowsuits, you should definitely size up! You need to account for the layers of clothing your baby will be wearing underneath. It’s better for a snowsuit to be a little roomy than to be too tight to zip up over their regular clothes. This is one area where buying for them to ‘grow into’ is a very smart strategy.