Baby Clothing Size Chart
Baby clothing labelled by age is one of the least reliable sizing systems in retail, because babies of the same age vary enormously in size and brands grade differently. This chart maps sizes to weight and height, which are what actually determine fit, along with realistic guidance on how many of each size to buy.
Sizes by weight and height
Preemie: up to 5 lbs / 2.3kg, up to 17 inches / 43cm.
Newborn (NB): 5-8 lbs / 2.3-3.6kg, 17-21 inches / 43-53cm. Many babies outgrow this in 2-4 weeks, and large newborns skip it entirely.
0-3 months: 8-12 lbs / 3.6-5.4kg, 21-24 inches / 53-61cm.
3-6 months: 12-16 lbs / 5.4-7.3kg, 24-26 inches / 61-66cm.
6-9 months: 16-20 lbs / 7.3-9kg, 26-28 inches / 66-71cm.
9-12 months: 20-24 lbs / 9-10.9kg, 28-30 inches / 71-76cm.
12-18 months: 24-28 lbs / 10.9-12.7kg, 30-32 inches / 76-81cm.
18-24 months: 28-30 lbs / 12.7-13.6kg, 32-34 inches / 81-86cm.
Why age labels mislead
Two healthy babies at six months old can differ by several pounds and inches, so an age label only describes an average. Always check the brand's weight and height range on the garment tag rather than buying by the month number on the front.
Brands also grade very differently: some run consistently small, others generous, and European sizing uses height in centimetres (56, 62, 68, 74) rather than age ranges at all, which is actually the more useful system. A 68cm label means the garment fits a baby up to 68cm tall, full stop.
How much to buy of each size
Newborn size is the one to buy sparingly: 4-6 bodysuits and sleepers at most, since many babies wear it only a few weeks and some never fit it. Accept hand-me-downs here rather than buying new.
0-3 and 3-6 months see the heaviest use, and with frequent changes from spit-up and blowouts most parents want 7-10 bodysuits and 5-7 sleepers per size.
From 6 months onward, babies stay in each size longer and change less often, so the same quantity stretches much further.
Practical buying notes
Size up rather than down when between sizes. A slightly large sleeper is safe and gets worn for months; a tight one is uncomfortable and wasted within weeks.
Buy ahead by season, not just size: a 6-9 month size bought in winter will be worn in summer, so think about what the baby will actually need at that weight rather than at that moment. Wash everything before first use, and skip anything with buttons on the back or complicated fastenings, since middle-of-the-night changes reward zips and snaps.