Baby Clothing Size Chart

Baby sizing is nominally by age in months, but weight is the more honest driver

Infant clothing labels read in months — "0-3 months," "6-9 months" — but newborns and infants vary enormously in birth weight and growth rate, meaning a label built around average age-in-months growth curves can be noticeably wrong for a baby who's born larger, smaller, or growing faster or slower than that average. Weight is the far more direct signal for baby clothing than it is for almost any other clothing category this site covers.

Newborn sizing exists as its own category below the standard age scale

Many brands print a distinct "Newborn" or "NB" size below "0-3 months," intended for a baby born at or under roughly 7-8 pounds (about 3.2-3.6kg) — a larger newborn can skip this size entirely and go straight into 0-3 months from birth, which is worth knowing before over-buying a size that may never fit.

Premature baby sizing is a distinct, separate category with its own chart

Preemie clothing is sized specifically for babies born significantly before term and well under standard newborn weight, using its own separate size scale entirely rather than simply the smallest end of the standard newborn range — a specialty preemie-specific brand or hospital-affiliated retailer is the right source here, not a general baby-clothing brand's smallest size.

EU baby sizing states height in centimetres more consistently than age

European infant clothing brands commonly print a height range in centimetres (for example, "56cm" or "62cm") as the primary size figure, often alongside rather than instead of an age range, because height correlates with actual body size more reliably across a population of babies than age in months does — measuring or estimating your baby's length is a stronger conversion signal into a EU brand's sizing than converting age alone.

Buying ahead for a fast-growing infant is standard practice, not overcaution

Because infants grow through multiple clothing sizes within their first year, often faster than the age labels alone suggest, buying one size ahead of a baby's current age/weight is routine practice among experienced parents rather than a sign the conversion itself was done wrong — this matters even more for gifts or seasonal clothing bought in advance of when it will actually be worn.

Sleep sacks, swaddles, and footed sleepwear size differently from daywear

A sleep sack or swaddle is sized around a snugger, safety-focused fit standard (to reduce loose fabric risk during sleep) rather than the room-to-grow assumption behind general daywear sizing, so converting a baby's general clothing size directly into a sleep-sack size can run too roomy — checking that specific sleep-product category's own weight and height chart is worth doing rather than assuming general baby-clothing logic applies.

Gifting sizes for a baby you haven't measured needs its own strategy

When buying a gift for a baby whose current height and weight you don't know precisely, sizing toward the upper end of the expected age range (or simply one size ahead of the baby's current age) is the more forgiving choice, since an infant garment that's briefly too big is far more usable than one that's already too small on arrival.

Snap and zip closures are placed for caregiver speed, not just fastening

Baby garments favor envelope necklines, wide snap closures, and full-length zips specifically so a caregiver can dress a squirming infant quickly and change a diaper without removing the whole outfit — this design detail doesn't affect the size conversion itself, but a garment lacking these features at the correct converted size can still be markedly less practical day to day.

Fabric weight for baby clothing varies by climate more than the label reflects

A baby garment labelled for a given age/weight range in a cold-climate market is often cut from noticeably heavier fabric than the nominally equivalent size from a warm-climate market's brand, since the base assumption about layering differs by region — checking fabric weight, not just the converted size number, matters when ordering baby clothing from a brand based in a very different climate than your own.

Hand-me-downs and multi-brand wardrobes make consistent sizing especially unreliable

Because baby clothing is so commonly passed between families, borrowed, or gifted from multiple different brands, a household's baby wardrobe often spans several brands' differing size interpretations at once — treating each brand's items on their own converted terms, rather than assuming one brand's "6 months" matches another's, avoids the common surprise of two same-labelled items fitting differently.

Baby shoes and soft-sole footwear sizing follows a separate scale entirely

Soft-sole crib shoes and early walking shoes for infants are generally sized by foot length in a scale distinct from the age/weight logic covering the rest of baby clothing, closer in spirit to the kids'-shoes chart elsewhere on this site — converting a baby's clothing size into a shoe size isn't a reliable shortcut, since the two follow entirely separate underlying measurements.

Christening and formal baby wear tolerates less buy-ahead margin than everyday onesies

A christening gown or formal baby outfit worn briefly for a single event benefits from being sized close to the baby's actual measurements at the time of the event rather than bought a size ahead the way an everyday onesie might be, since there's no later opportunity to "grow into" a garment worn once on a specific date.

Head circumference matters separately for hats, hooded outfits, and swaddle openings

A baby's head circumference doesn't scale in lockstep with the rest of the body the same way it does for older children and adults, so a hooded baby outfit or infant hat converted purely off a general age/weight size can still bind or gap around the head — checking a head-specific circumference figure, where a brand publishes one, is worth the extra step for hooded and hatted infant pieces specifically.

Growth centile charts, not a fixed baby-clothing standard, sit behind most brands' age labels

A baby-clothing brand's age-to-size assumption is typically built from national or regional paediatric growth centile data, which differs somewhat between countries and even between different reference populations used decades apart, so two brands from different countries both claiming to use 'average growth data' for the same age can still land on measurably different size assumptions.

Twin or closely-spaced siblings sharing hand-me-downs need individual tracking, not a shared assumption

Baby clothing passed between twins or closely-spaced siblings is easy to assume will fit similarly since the children share an age or a close one, but individual infants vary enough in growth rate that tracking each child's own current size separately, rather than assuming a shared wardrobe transfers cleanly, avoids the common surprise of one twin fitting a hand-me-down while the other doesn't.

A hospital-issue newborn outfit is not a reliable size reference for shopping afterward

The tiny outfit a baby wears home from the hospital is often a hospital-branded or gifted sample sized generously for a wide range of newborns rather than fitted specifically, so treating that outfit's tag as a genuine size reference for a follow-up purchase can be misleading — an actual weight taken at a pediatrician visit is a more dependable figure to shop from in the first weeks.