Sizing & fit
Baby between two sizes: when to size up and when not to
Sizing up is the usual rule, but not for everything. How to choose between two sizes for sleepsuits, daywear, winter layers and outfits for a special day.
The usual rule, and why it has exceptions
Our size guide’s advice for a baby between sizes is to choose the larger one, and for most everyday clothes that holds: babies grow fast, and the bigger size gets more wear. But “between sizes” means different things for different pieces. A little extra room is fine in joggers, useful in a winter jumpsuit and a poor idea in something your baby sleeps in, so decide piece by piece rather than applying one rule to the whole order.
Start by measuring. If their length sits at the top of one range and their weight at the bottom of the next, you are genuinely between sizes. If only their age says so, check the size guide first; you may not be between sizes at all.
Two-piece sets and daywear: size up
Separates are the most forgiving. Where there are ribbed cuffs, they hold sleeves and legs in place, so a little extra length can be turned back once and still look neat, and an adjustable or elasticated waist copes with a waist that is ahead of the legs or behind them. A set like our Navy Moon & Stars Henley & Jogger Set, with drawstring joggers, will look slightly relaxed at first in the larger size and fit properly within weeks.
The one thing to watch is hem length once your baby is crawling or pulling up to stand. Trousers that pool over the feet get caught under knees and heels, so turn them up or keep them for later.
Sleepsuits for night-time: the fit you have now
For sleep, choose the size that fits your baby today, or one that is only slightly roomy. A sleepsuit that is a whole size too big has spare fabric at the neck and sleeves that can bunch up, and feet so long that your baby’s own feet slide around inside. Safer-sleep advice from the NHS and The Lullaby Trust centres on keeping a baby’s face and head clear and not letting them overheat, and a well-fitting sleepsuit sits better with both than a baggy one.
Keep the bigger size for daytime until it fits properly.
Winter outer layers: size up
A hooded jumpsuit goes over other clothes, so it needs room for a sleepsuit or a knit set underneath. If your baby is between sizes, the larger jumpsuit, such as our Grey Bear Hooded Jumpsuit, is the practical choice, and a small baby may get a second winter out of it. Our post on which jumpsuit size to buy for a first winter covers leaving room for the layers underneath.
Outfits for a date on the calendar: fit on the day
For an aqiqah, Eid or a wedding, the question is not which size fits now but which will fit on the day. Estimate their length on that date and buy for it. An outfit that looks right in the photos matters more here than one that lasts for months, so do not size up twice to be safe. Our post on buying for next season walks through the same kind of estimate.
Footed pieces: let the toes decide
With covered feet, the deciding measurement is often the foot rather than the body. If their toes already touch the end when their legs are gently straightened, go up a size even if the snaps still close easily. If the body is loose and the feet are fine, stay where you are.
Sources
NHS and The Lullaby Trust, safer sleep and overheating advice.
Quick answers
Is it bad for a baby to wear clothes that are too big?
For daytime, a little extra room is fine as long as sleeves don’t cover their hands all day and hems don’t catch a crawler or walker. For sleep, choose a sleepsuit that fits now rather than one a size too big.
My baby is right on the line between 3–6M and 6–12M. Which should I buy?
For sets and outer layers, 6–12M. For sleepsuits, try the 3–6M first: if the snaps close easily and the toes have room, it will do for nights for a few more weeks before the 6–12M takes over.
Can I size down if the bigger size swamps my baby?
Yes, if the smaller size fits their length with a little room to spare. Size down only when the smaller piece is comfortable now; one that is already snug will be outgrown within weeks.
