Baby clothing sizing is one of the most confusing parts of shopping for a new arrival — and it gets more confusing when you're shopping across different brands or countries. A size "3–6 months" from one brand can fit very differently from another, and US, UK and EU sizing systems don't always line up neatly. This complete baby girl size guide breaks it all down so you can shop with confidence, get the right fit first time, and stop returning clothes that don't fit.
Why Baby Clothing Sizes Are So Inconsistent
Unlike adult clothing, baby sizing has no universal standard. Brands base their sizing on different reference measurements — some use age, some use height in centimetres, and some use a combination of both. A "6 month" size from a US brand may correspond to a "6–9 month" size from a UK brand and a "68cm" size from a European brand — all referring to roughly the same baby.
The most reliable way to shop for baby clothing is always to use height in centimetres as your primary reference, then cross-check with the brand's own size chart where available. Age is a rough guide only.
How to Measure a Baby for Clothing
You only need a soft measuring tape and ideally a second pair of hands. Measure when the baby is calm — lying down works best for newborns and young infants.
Height / Length
Lay the baby flat on her back on a firm surface. Gently straighten her legs and measure from the top of her head to the bottom of her heel. This is the most important measurement for sizing — more reliable than age at every stage.
Chest
Measure around the fullest part of the chest, keeping the tape parallel to the surface. Keep it snug but not tight. This matters most for tops, rompers and dresses.
Weight
Some brands include weight as part of their size guide, particularly for newborn and 0–3 month sizes. A baby's weight at birth gives a useful starting point but becomes less reliable as a sizing reference after the first few weeks.
Remeasure every 6–8 weeks for the first year — babies grow fast and a size that fits perfectly one month may be too small the next.
Baby Girl Size Chart — Newborn to 24 Months
| US Size | UK Size | EU Size | Height (cm) | Height (inches) | Weight (approx) | Age (guide only) |
|---|---|---|---|---|---|---|
| Newborn | Newborn | 50–56 | 50–56 cm | 20–22" | Up to 4.5 kg / 10 lbs | 0–1 month |
| 0–3M | 0–3M | 56–62 | 56–62 cm | 22–24" | 4.5–6 kg / 10–13 lbs | 1–3 months |
| 3–6M | 3–6M | 62–68 | 62–68 cm | 24–27" | 6–8 kg / 13–17 lbs | 3–6 months |
| 6–9M | 6–9M | 68–74 | 68–74 cm | 27–29" | 8–9.5 kg / 17–21 lbs | 6–9 months |
| 9–12M | 9–12M | 74–80 | 74–80 cm | 29–31" | 9.5–11 kg / 21–24 lbs | 9–12 months |
| 12–18M | 12–18M | 80–86 | 80–86 cm | 31–34" | 11–12.5 kg / 24–27 lbs | 12–18 months |
| 18–24M | 18–24M | 86–92 | 86–92 cm | 34–36" | 12.5–14 kg / 27–31 lbs | 18–24 months |
Age ranges are approximate guides only. Always use height as your primary sizing reference.
US vs UK vs EU Baby Sizing — What's the Difference?
US Baby Sizing
US sizing uses age ranges as the primary label — Newborn, 0–3M, 3–6M, 6–9M, 9–12M, 12–18M, 18–24M. US sizing tends to run slightly larger than UK sizing in the early months, so a US 3–6M may fit a baby who is technically in the UK 3–6M range but on the larger end.
UK Baby Sizing
UK sizing uses the same age-range labels as US sizing and is broadly comparable. The key difference is that UK sizes sometimes run slightly smaller in the 0–6 month range. If you're ordering from a UK brand, it's worth checking the centimetre measurement rather than relying on the month label alone.
EU Baby Sizing
European sizing uses height in centimetres as the label — 50, 56, 62, 68, 74, 80, 86, 92. This system is actually the most intuitive once you know your baby's height, because it maps directly to her measurements rather than an age estimate. EU size 68 = a baby who is approximately 68cm tall.
Browse our baby and newborn clothing collection — all products include height-based sizing to make it easy to find the right fit.
How Long Does a Baby Stay in Each Size?
This varies enormously from baby to baby, but here's a general guide based on typical growth patterns:
- Newborn: 0–4 weeks — many babies skip this size entirely if born above average weight
- 0–3 months: 4–12 weeks — usually about 6–8 weeks of good wear
- 3–6 months: 2–3 months of wear — one of the best sizes to stock up on
- 6–9 months: 2–3 months — growth starts to slow slightly
- 9–12 months: 2–4 months — some babies stay in this size longer
- 12–18 months: 3–6 months — growth rate slows considerably
- 18–24 months: 4–6 months — by this stage most clothing gets good wear before being outgrown
The practical takeaway: don't over-buy in any single size, especially newborn. Buy a few pieces in the current size, stock up slightly in the next size up, and shop little and often as she grows.
What Size Should You Buy as a Baby Gift?
If you're buying a gift and don't know the baby's exact measurements, the 3–6 month or 6–9 month size is almost always the safest choice. Most babies outgrow newborn clothing within weeks, so gifting a slightly larger size means the outfit will actually get worn properly rather than being outgrown before it's used.
If you know the baby's due date, think about what size she'll be in when the weather changes — a summer romper in 3–6 months is perfect for a spring baby, but a summer baby might need 6–9 months to make it to the warmer weather in that size.
For more gift ideas, read our complete baby shower gift guide for girls.
Tips for Getting the Best Fit
Always size up when in doubt
A slightly larger size is always preferable to something too small. Babies grow into clothes; they don't shrink. Look for styles with elasticated waists, adjustable ties, and snap fastenings that give a little flexibility across sizes.
Check the height, not just the age label
Two babies of the same age can differ by several centimetres in height. Always match your baby's current height to the size chart rather than assuming her age corresponds to the size label.
Account for nappies
Babies wear nappies under their clothing — which adds bulk around the waist and bottom. If a size fits perfectly over bare skin, it may be too tight with a nappy. This is especially relevant for fitted styles, trousers, and rompers with snap fastenings at the bottom.
Cotton can shrink slightly
Cotton garments may shrink slightly after the first wash if washed in hot water. Wash on a cool cycle (30°C / 86°F) and avoid tumble drying on high heat to maintain the original size and shape.
Frequently Asked Questions
What size does a newborn baby girl wear?
Most newborn babies wear Newborn or 0–3M sizing, which corresponds to a height of 50–62cm. Babies born above average weight — over 4 kg or 8.8 lbs — may go straight into 0–3M and skip the Newborn size entirely.
How long does a baby stay in 0–3 month clothes?
Most babies stay in 0–3 month clothing for approximately 6–8 weeks. Larger babies may outgrow it sooner; smaller babies may wear it a little longer. It's one of the fastest-outgrown sizes, so avoid buying too many pieces in this range.
What is the difference between US size 6M and EU size 68?
US size 6M (6 months) and EU size 68 refer to roughly the same baby — approximately 62–68cm in height and 6–9 months old. The EU size uses the baby's height in centimetres as the label, making it slightly more precise than the US age-based system.
What size baby clothes should I stock up on?
The 3–6 month and 6–12 month sizes offer the best value — babies spend more time in these sizes than newborn, and the clothing gets properly worn before being outgrown. These sizes are also the best choices for gifts.
Do baby clothes sizes vary between brands?
Yes — significantly. Two brands can label the same size differently, and cuts vary considerably. Always use the height measurement in centimetres as your reference rather than relying on the size label alone. When in doubt, size up.
What size is a 12-month-old baby girl in EU sizing?
A 12-month-old baby girl typically wears EU size 74–80, which corresponds to a height of approximately 74–80cm. This is equivalent to US/UK size 9–12M or 12–18M depending on her height.
Shop Baby Girl Clothing by Size at Tots America
At Tots America all baby and newborn clothing includes clear height-based sizing so you always know exactly what you're buying. From newborn rompers and cotton sets to lace-trim tights and three-piece gift sets, every piece is designed to be soft, practical and genuinely adorable.
- Baby and newborn clothing — 0 to 24 months
- Girls clothing — 2 to 6 years
- Girls clothing — 6 to 14 years
- New arrivals — latest styles across all ages
Free shipping on all orders over $30. New styles added every week — shop Tots America.
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