How Baby Clothes Sizes Work
A Simple Guide for Parents (Without the Guesswork)
If you’ve ever stared at a baby grow wondering how a seven-pound newborn is supposed to fit in something marked "0–3 months," you’re not alone. Baby clothes sizes can feel a little all over the place. And often, they are. The truth is, every baby grows differently, and every brand sizes their clothes a little differently too. So what are you supposed to do?
We’re here to help. This guide breaks down how baby clothes sizing works, shares our own size chart, and offers real-world advice to help you feel more confident when choosing outfits for your little one.
What Do Baby Clothes Sizes Actually Mean?
Most baby clothing is sized by age ranges: 0–3 months, 3–6 months, 6–9 months and so on. But those numbers are only rough guidelines. Some babies never wear "newborn" at all. Others are still in 3–6 months when they’re nearly one. And that's perfectly normal.
Because baby clothes sizing depends on more than just age. It also depends on weight, height, and how the clothes are made. Which is why we design all Lottie & Lysh clothing with a bit of growing room in mind.
Lottie & Lysh Baby Clothes Sizing Guide
Below is our sizing chart, created using measurements we've refined over years of designing for real babies (and their growth spurts). If you're unsure which size to go for, we always recommend sizing up for extra wear time.
| Size | Waist (in/cm) | Chest (in/cm) | Height (in/cm) | Inseam (in/cm) | Head (in/cm) |
|---|---|---|---|---|---|
| Preemie | 14" (35.5) | 13.75" (35) | 17.5" (44) | 5" (13) | 13.75" (35) |
| Newborn | 16" (40.75) | 15.5" (39.25) | 20.5" (52) | 6.75" (17) | 15" (38) |
| 0–3 M | 17.5" (44.5) | 17" (43.25) | 24" (62) | 8.5" (21.5) | 16.5" (42.25) |
| 3–6 M | 18.5" (47) | 18" (45.75) | 27" (68) | 10" (25.75) | 17.5" (44.75) |
| 6–9 M | 19" (48.25) | 18.5" (47) | 28.5" (72) | 11.25" (28.5) | 18" (45.75) |
| 9–12 M | 19.5" (49.5) | 19" (48.25) | 30.5" (78) | 12.5" (31.75) | 18.5" (47.25) |
| 12–18 M | 20.25" (51.5) | 19.75" (50.25) | 33" (84) | 13.5" (34.25) | 19" (48.5) |
| 18–24 M | 21" (53.25) | 20.5" (52) | 35" (90) | 14" (35.5) | 19.5" (49.5) |
| 2–3 Y | 21.5" (54.5) | 21" (53.25) | 37" (94) | 15.25" (38.75) | 20" (50.75) |
| 3–4 Y | 22" (56) | 22" (56) | 41" (104) | 17.5" (44.5) | 20.5" (52) |
| 4–5 Y | 22.5" (57.25) | 23" (58.5) | 44" (110) | 18.75" (47.5) | 20.75" (52.75) |
| 5–6 Y | 23" (58.5) | 24" (61) | 46.5" (118) | 20.25" (51.5) | 21" (53.25) |
Our Best Advice: Think Fit + Function
We always design with real babies (and real life) in mind. That means:
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Our rompers and jackets are made to last through multiple size stages.
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Many styles feature adjustable cuffs and longer lines for extra growing room.
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All fabrics are soft, breathable, and OEKO-TEX certified. So even if a little snug, they’re still comfy on delicate skin.
Need a visual? Our Bonnie Bunny Jackets are a great example. Turn-up cuffs, longline fit, plenty of room to grow.
Planning Ahead? Don’t Miss This:
If you're shopping before baby arrives, you might be wondering what size clothes to pack for the hospital. Our hospital bag checklist has everything you need. Including sizing tips, outfit suggestions, and the practical things people often forget.
Still Unsure? We’re Here for You
If you’re choosing a gift, a going-home outfit, or building your baby’s first wardrobe, feel free to reach out. You can message us directly with sizing questions. We’re real people who make real clothes, and we’re happy to help.
Want to get started? Explore our collections:
We know it can feel like guesswork. But with a little help and a lot of softness, we promise you’ll get it just right.
FAQs About Baby Clothes Sizing
How do I know what size baby clothes to buy?
Use our baby size chart as a guide. If your baby is between sizes or close to the top end of a range, we always recommend sizing up for extra comfort and wear time.
What size baby clothes should I pack in my hospital bag?
We suggest bringing both Newborn and 0–3 months. Babies come in all shapes and sizes, and it’s good to be prepared with a back-up size just in case.
Are your baby clothes true to size?
Our clothes are generously sized with added room to grow. Most styles have turn-up cuffs and longline fits to give you longer use.
