Baby Clothes Sizes by Age: Chart + Free Calculator – Babbez

B By the Babbez team · Baby-clothing specialists · August 2026 · 6 min read

Quick answer: Baby clothes are labeled by age, but weight and height are the more reliable guide. Newborn fits roughly 6–9 lb, 0–3M about 9–12.5 lb, and 3–6M about 12.5–17 lb. Most babies move up a size sooner than the label suggests — when in doubt, size up. Use the calculator below or the full chart to find your baby's size in seconds.

If you've ever bought a "3-month" outfit that didn't fit at 3 months, you're not alone — it's one of the most common reasons baby clothes get returned. The fix is simple: size by your baby's weight and height, not just their age. This guide gives you an instant calculator, the full age-weight-height chart, how much to buy in each size, and exactly when to move up.

Key takeaways

Age is a starting point; weight is the most accurate signal for baby clothing size.
Sizes are ranges with overlap — a big newborn may skip Newborn and start at 0–3M.
Size up for comfort, longer wear, and bulky items like snowsuits and outerwear (sleepwear is the exception — see below).
Sizes vary by brand — always check the label's weight/height range, not just the age.

Free tool

Baby Clothing Size Calculator

Baby clothing size chart by age, weight & height

Here is the full baby and toddler clothing size chart. Match your baby's weight first, then height, then age — if two disagree, choose the larger size for comfort and growing room. (Newborn covers birth to about 1 month, so the 0–3M size starts around 1 month.)

Baby clothing size chart — age, weight and height by size. Swipe sideways to see every column.
Size	Age	Weight (lb)	Weight (kg)	Height (in)
Preemie	preemie	up to 6 lb	up to 2.7 kg	up to 17"
Newborn	up to 1m	6–9 lb	2.7–4.1 kg	17–21.5"
0–3M	1–3m	9–12.5 lb	4.1–5.7 kg	21.5–24"
3–6M	3–6m	12.5–17 lb	5.7–7.7 kg	24–26.5"
6–9M	6–9m	17–21 lb	7.7–9.5 kg	26.5–28.5"
9–12M	9–12m	21–25 lb	9.5–11.3 kg	28.5–30.5"
12–18M	12–18m	25–28 lb	11.3–12.7 kg	30.5–32.5"
18–24M	18–24m	28–30 lb	12.7–13.6 kg	32.5–34"
2T	24–36m	30–33 lb	13.6–15 kg	34–36"
3T	36–48m	33–36 lb	15–16.3 kg	36–38.5"
4T	48–60m	36–40 lb	16.3–18.1 kg	38.5–41"

These are clothing-fit ranges, not growth targets or medical advice — every baby grows differently. For questions about your baby's growth, ask your pediatrician.

How do baby clothing sizes work?

Baby clothes are sized in age bands — Newborn, 0–3M, 3–6M, and so on — but each band is really a weight and height range. Because babies grow at very different rates, two babies of the same age can wear sizes months apart. That's why the label always lists a weight range: it's the number to trust over the printed age.

After 24 months, sizing switches to toddler "T" sizes (2T, 3T, 4T). These are cut for a taller, more active toddler with room for a diaper, so a 2T fits differently from a 24-month piece even though the ages overlap.

Should you size up in baby clothes?

In most cases, yes. Babies grow fastest in the first year, and roomier clothes are more comfortable and last longer. Size up when your baby is in the top third of a weight range, for outerwear and snowsuits, and for brands known to run small.

The Babbez size-up rule

If your baby's weight or height sits in the upper third of a size band, buy the next size up too — you'll get weeks of extra wear instead of packing away barely-worn outfits. For snowsuits, coats, and layering pieces, size up by default. Sleepwear is the exception: under the U.S. CPSC flammability rule (16 CFR 1615/1616), non-flame-resistant baby sleepwear is made to fit snugly and carries a snug-fit safety label — follow the garment's own sizing there rather than sizing up.

How many clothes do you need in each size?

Babies go through 2–3 outfits a day, so plan around laundry every 2–3 days. The quantities below cover the busiest first-year sizes — buy the fewest in Newborn (many babies wear it only a week or two) and the most in 0–3M and 3–6M, the sizes they stay in longest.

How many of each item to buy, by size (first year).
Size	Bodysuits	Sleepers	Outfits	Notes
Newborn	4–6	4–6	2–3	Buy light — many skip it
0–3M	7–10	6–8	4–6	The workhorse size
3–6M	7–10	6–8	4–6	Long-wear size
6–12M	6–8	5–6	4–5	Add weather layers

Do baby clothing sizes differ by brand?

Yes — sizing is not standardized, so a 3–6M from one brand can fit like a 6–9M from another. Always check the garment's stated weight and height range rather than the age on the front, and when a brand is known to run small, size up.

When should you move up a size?

Move up when outfits feel snug at the shoulders or thighs, when snaps strain at the crotch, when sleeves and legs ride up, or when your baby reaches the top of the current size's weight range. Re-check the fit every 4–6 weeks in the first year.

How do European (cm) baby sizes convert to US sizes?

European baby sizes are simply the child's height in centimeters — a size 62 fits a baby up to about 62 cm tall. That makes them easy to use: measure your baby's length, pick the number at or just above it, and go up if you are between numbers. Many Babbez pieces are labeled by age with the EU cm size alongside, so one table covers both.

EU size (cm)	Closest US size	Approx. age
50–56	Newborn	0–1 month
56–62	0–3M	1–3 months
62–68	3–6M	3–6 months
68–74	6–9M	6–9 months
74–80	9–12M	9–12 months
80–86	12–18M	12–18 months
86–92	18–24M / 2T	18–24 months
92–98	2T–3T	2–3 years

How to measure your baby

Lay your baby flat on a blanket, gently straighten one leg, and measure from the crown of the head to the heel — that length in centimeters is the EU size to buy at or just above. For weight, the number from the most recent checkup is accurate enough; sizes are ranges, so precision to the ounce does not matter. Brand charts still vary, so check each label's own range exactly as you would with the US chart above.

Frequently asked questions

What size does a newborn wear?

Most newborns wear Newborn size (about 6–9 lb, up to 21.5"), but babies over ~8 lb at birth often go straight into 0–3M. Buy only a few Newborn pieces — many babies outgrow it within two weeks.

Is baby clothing sized by age or weight?

Both are printed, but weight (and height) is the reliable guide. The age on the label is an average; the weight range tells you whether it will actually fit your baby.

What size comes after 24 months?

Toddler sizes: 2T, 3T, then 4T. They overlap with 18–24M by age but are cut roomier for a walking, potty-training toddler.

Should I size up in baby sleepwear?

Not by default. Under the U.S. CPSC flammability rule, non-flame-resistant baby sleepwear (above 9 months) is made to fit snugly as a safety feature and carries a snug-fit label — so follow the garment's own size guide for sleepwear rather than sizing up. Sizing up is fine for daywear and outerwear.

What size is 80 in baby clothes?

Size 80 is a European size based on height: it fits a baby up to about 80 cm (31.5") tall, which for most brands corresponds to roughly 12 months — a US 9–12M or 12–18M depending on the brand's cut. EU sizes are the baby's height in centimeters, so measure your baby's length and choose the number at or just above it.

Now you know the size — shop it.

Browse Babbez baby clothing by exact size, from Newborn to 4T.

Shop baby clothes by size →

This guide gives general sizing information to help you shop and reduce returns — it is not medical or growth advice. Every baby grows differently and clothing sizes vary between brands. Sizing reflects standard US baby and toddler apparel ranges. Sleepwear is a special case: under the U.S. CPSC flammability rule, non-flame-resistant baby sleepwear is required to fit snugly, so always follow the manufacturer's sizing and safety label. See our full medical disclaimer.

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