Baby Clothes Size Chart by Weight (Newborn–24 Months)

If you’ve ever held up a tiny onesie and thought, “There’s no way my baby is going to fit in this,” you’re not alone. Baby clothing sizes can feel confusing, especially because “3 months” doesn’t always mean your baby is three months old, and two babies the same age can be totally different shapes.

Here’s the gentle truth, mama-to-mama: weight and length are the most reliable way to choose baby clothes sizes. Age labels can be a helpful starting point, but they’re not the deciding factor.

This guide will give you a simple baby clothes size chart by weight (newborn through 24 months), plus quick fit tips for when your baby is between sizes so you can shop with confidence and avoid the “too small on day one” frustration.

If you’re shopping by age on our site, you can also jump straight to your baby’s current size collection, like 0–3 month clothes, 3–6 month clothes, or 6–9 month clothes.

If you want the simplest plan:

• Use baby’s current weight as your main anchor
  
  

• Use length as your tie‑breaker when you’re between sizes
  
  

• If baby is close to the upper end of a size, go up (especially for footies and sleepers)
  
  

• If baby is slim/small and you want the best fit right now, stay true to size
  
  

And remember: the “right” size is the one that fits your baby today, not the one you hope they grow into next month.

These ranges are a general guide (because brands vary), but they’re a helpful starting point when you’re choosing between Newborn, 0–3, 3–6, and beyond.

• Newborn: ~6–9 lb (2.7–4.1 kg) | ~18–21 in (46–53 cm)
  
  

• 0–3 months: ~9–12 lb (4.1–5.4 kg) | ~21–24 in (53–61 cm)
  
  

• 3–6 months: ~12–16 lb (5.4–7.3 kg) | ~24–26 in (61–66 cm)
  
  

• 6–9 months: ~16–20 lb (7.3–9.1 kg) | ~26–28 in (66–71 cm)
  
  

• 9–12 months: ~20–24 lb (9.1–10.9 kg) | ~28–30 in (71–76 cm)
  
  

• 12–18 months: ~24–28 lb (10.9–12.7 kg) | ~30–32 in (76–81 cm)
  
  

• 18–24 months: ~28–32 lb (12.7–14.5 kg) | ~32–34 in (81–86 cm)
  
  

If your baby falls between two size ranges (super common), use the “between sizes” tips below.

You only need two numbers:

1) Weight
 Use baby’s most recent weight (or a quick home check). Weight is the most reliable anchor for baby sizing.

2) Length
 Measure baby from the top of the head to the heel (or shoulder to heel, either works if you’re consistent). Length is the best tie‑breaker when weight sits in an overlap.

One quick tip: if your baby is long for their weight, you may need to size up sooner in sleepers and footies—even if the waistband sizes still fit.

If baby is between sizes, don’t panic, this is where most parents live.

Use these gentle tie‑breakers:

• If your baby is near the top of the weight range, size up
  
  

• If your baby is long (even if weight is lower), size up for comfort
  
  

• If your baby is petite and you want the best fit right now, stay true to size
  
  

And here’s the mama tip no one tells you: some pieces run more forgiving than others… which brings us to:

Not all baby clothes fit the same, even in the same size.

Bodysuits
Bodysuits can feel snug around the diaper area when baby grows quickly. If snaps are pulling or you’re fighting the crotch closure, it’s time to size up.

Footies and sleepers
Footies tend to get outgrown by length first. If baby’s toes are pressing into the bottom, it’s time to size up, especially for overnight comfort.

Two‑piece sets
Two‑piece outfits can be more flexible because the top and bottoms don’t need the same “full‑body” length. If your baby is long, two‑piece sets can sometimes fit longer than footies in the same labeled size.

Newborn

Newborn sizes can be outgrown quickly. If you’re expecting an average or bigger baby, it’s completely normal to use Newborn for a short window and live mostly in 0–3 month clothes.

0–3 months

This is one of the most-used sizes for many families because it gives baby room to grow while still feeling snug and cozy.

3–6 months

This is often the “settled” size—baby starts to feel sturdier, and you’ll likely get a nice amount of wear out of this range.

6–9 months and 9–12 months

This is when mobility ramps up (rolling, crawling, standing), so comfort and flexibility matter a lot. Pieces that feel soft and breathable tend to get worn constantly.

12–18 months and 18–24 months

Toddlers start developing strong opinions. This is where easy on/off outfits and comfy sets shine, especially if you’re heading toward potty training soon.

If you’re building a wardrobe without going overboard, here’s a gentle approach:

• Start with the size your baby fits right now
  
  

• Buy a smaller “backup” set in the next size up (so you’re not caught off guard)
  
  

• Restock after you see how fast your baby grows and how often you do laundry
  
  

If you want a more complete wardrobe guide, you can link to your post How Many Outfits Does a Newborn Need? 

If you want a simple, high-use wardrobe that covers most days:

• Start with baby clothes basics.

• Add a rotation of baby pajamas for nighttime

• Keep baby bodysuits as your base layer 

• If sleep is your current season, pair pajamas with a baby sleep sack

This keeps it simple and makes bedtime routines easier, without buying random pieces you won’t reach for.

If you remember one thing from this post, make it this: use weight as your anchor, length as your tie‑breaker, and trust the fit you see on your baby.

And if you want the easiest shopping experience, start with your baby’s current size collection (like 0–3 month clothes or 3–6 month clothes) and build a small rotation of the pieces you’ll actually use every week.