Baby Clothes: Sizing, Fabric, and Why Nothing Fits
Baby clothing sizing is guidance rather than measurement, and every brand interprets it differently. A newborn size in one label fits a different baby to a newborn size in another. This is the main reason parents end up with drawers of unworn clothing in sizes that were skipped entirely.
How baby sizing actually works
Most brands size by age band — newborn, 0–3 months, 3–6 months — but the underlying measurement is length and weight, and those are what the size chart lists if you look. Babies vary enormously at the same age, so the age on the label is the least useful number on it.
- Check the length and weight range on the brand's chart, not the age band.
- Size up if you are between. A slightly large sleepsuit is wearable; a slightly small one is not, and the baby is growing towards the larger size anyway.
- Expect brands to differ by a full size. If a brand fits well, note it. That knowledge is worth more than any review.
- Buy ahead sparingly. Guessing which size a baby will be in a given season rarely works out.
Fabric: what survives the wash
Baby clothes are washed constantly, often hot, and that is what determines whether they last past the size.
- Cotton — the default for good reason: breathable, soft, washes hot. It shrinks, so a first wash at the temperature you intend to use is a fair test.
- Cotton with a little elastane — keeps shape through repeated washing and makes getting a wriggling baby dressed easier.
- Bamboo viscose — very soft and popular for sleepwear. Usually needs gentler washing, which is a real consideration for an item that will be washed constantly.
- Polyester fleece — warm and quick to dry, less breathable. Fine for outer layers, less good next to skin.
- Wool — excellent temperature regulation, but check whether it is machine washable before buying, because most is not.
The care label is worth reading before you buy rather than after. An item that needs a cold gentle cycle will either not get washed properly or will not survive being washed the way everything else is.
Details that matter more than they sound
- Envelope necklines on bodysuits let you take them off downwards, which matters more than you would think.
- Poppers rather than buttons along the legs — you will be doing this in the dark.
- Two-way zips on sleepsuits open from the bottom for a nappy change without undressing the whole baby.
- Fold-over cuffs save buying scratch mittens that fall off.
- Flat seams against the skin, particularly for anything worn for sleep.
How many you actually need
For a newborn, roughly five to seven bodysuits and the same number of sleepsuits covers a normal laundry cycle. Add more only if you are washing less often than every other day. Everything beyond that is either a gift or a purchase you make once you know your baby's size.
Outerwear is the exception in the other direction: a baby needs one good warm layer, not several. And avoid thick padded coats for anyone travelling in a car seat, since bulky layers interfere with harness fit.
Before you order
Check the return window, because baby clothing is often bought ahead and the window can expire before the size is needed. Check whether the retailer accepts returns on washed items — they generally do not, so try things on before washing. And where a brand runs large or small, the reviews will usually say so; that single line is more useful than the size chart.