One of the most confusing aspects of buying baby clothes is figuring out sizes. Between Australian sizing systems, American and European imports, and massive brand-to-brand variations, getting the right fit can feel like solving a puzzle. Add in the fact that babies grow at wildly different rates, and it's no wonder so many parents end up with wardrobes full of clothes that were never worn.
This comprehensive size guide will help you navigate baby clothing sizes with confidence, ensuring you buy clothes that actually fit your baby—and get worn before they're outgrown.
Understanding Australian Baby Sizes
Australia uses a numerical sizing system for baby clothes that differs from the US and UK. Here's how the standard Australian baby sizes work:
Standard Australian Size Chart
- Size 0000 (Premature/Newborn): Up to 3kg / Up to 50cm height
- Size 000 (0-3 months): 3-6kg / 50-62cm height
- Size 00 (3-6 months): 6-8kg / 62-68cm height
- Size 0 (6-12 months): 8-10kg / 68-76cm height
- Size 1 (12-18 months): 10-12kg / 76-84cm height
- Size 2 (18-24 months): 12-14kg / 84-92cm height
These sizes are guidelines based on average baby measurements. Your baby may fit sizes differently based on their individual proportions—some babies are long and lean, others are shorter and chunkier.
Weight is often a better indicator of size than age, especially in the first year. A 3-month-old who weighs 7kg might fit better in size 00 (3-6 months) than size 000 (0-3 months).
How to Measure Your Baby
To get the most accurate size, you'll need three measurements. It's easiest to do this when your baby is relaxed and lying down.
Height/Length
Lay your baby flat on their back on a firm surface. Gently straighten their legs and measure from the top of their head to the bottom of their heel. Having a second person hold baby still can help.
Weight
Use your baby's most recent weight from a health check, or weigh yourself holding baby, then subtract your weight. Baby scales at pharmacies or child health clinics provide the most accurate readings.
Head Circumference
Wrap a soft measuring tape around the widest part of your baby's head, usually just above the eyebrows and ears. This measurement is important for hats.
Always measure your baby before buying clothes online. Babies grow in spurts, and the size they wore last month might not be accurate today.
International Size Conversions
When buying from international brands, you'll encounter different sizing systems. Here's a rough conversion guide:
US/UK Sizes
- Newborn = Australian 0000-000
- 0-3M = Australian 000
- 3-6M = Australian 00
- 6-9M = Australian 0 (smaller end)
- 9-12M = Australian 0
- 12-18M = Australian 1
- 18-24M = Australian 2
European Sizes
European sizing is based on height in centimetres, which is actually quite practical:
- Size 50 = Australian 0000
- Size 56 = Australian 000
- Size 62 = Australian 000-00
- Size 68 = Australian 00
- Size 74 = Australian 0
- Size 80 = Australian 0-1
- Size 86 = Australian 1
These conversions are approximate. Some international brands run larger or smaller than Australian standards, so always check the brand's specific size chart when available.
Why Sizes Vary Between Brands
If you've ever noticed that your baby fits a size 00 in one brand but needs a size 0 in another, you're not imagining things. Brand-to-brand variation is very real, and here's why:
- Target market: Brands targeting different demographics may cut sizes differently
- Country of origin: Brands from different countries use different base measurements
- Fit philosophy: Some brands design for a roomy fit, others for a snugger fit
- Fabric stretch: Stretchy fabrics are often cut smaller, assuming they'll expand
- Pre-shrinkage: Some brands account for shrinkage, others don't
Once you find brands that fit your baby well, stick with them. It's worth noting which brands run large or small so you can adjust when shopping.
Shopping Strategies for Better Fit
Don't Buy Too Far Ahead
It's tempting to stock up on future sizes, especially when you see a good sale. But babies grow unpredictably, and seasonal timing matters. That winter jacket in size 1 might not fit when winter actually arrives.
A safe approach is to buy no more than one size ahead, and stick to basics rather than seasonal items.
When in Doubt, Size Up
Babies grow quickly, and slightly too-big clothes will eventually fit. Slightly too-small clothes will never be worn. When you're unsure between sizes, choose the larger one.
Consider Adjustable Features
Some baby clothes have features that extend their wearable life:
- Roll-up cuffs on sleeves and pants
- Adjustable waistbands
- Expandable necklines
- Extra snap positions on bodysuits
Keep Tags On Until You're Sure
Don't remove tags until you've checked the fit. Many stores accept returns of unworn items with tags attached, which gives you flexibility if the size is wrong.
Size Considerations by Garment Type
Bodysuits and Onesies
These should fit snugly enough that they don't bunch up under clothes, but loose enough to fasten comfortably at the crotch. If the snaps are straining, it's time to size up.
Sleepwear and Sleep Sacks
Sleep sacks should fit correctly for safety. The neck hole should be small enough that your baby's head cannot slip inside. Check the manufacturer's weight guidelines carefully.
Pants and Leggings
Baby pants should allow for a nappy. If they fit perfectly without a nappy, they'll likely be too tight with one. Also consider whether your baby is crawling—they may need more room in the knees.
Hats
Hat sizes are based on head circumference. A too-tight hat will leave marks on baby's head; a too-loose hat will fall over their eyes. Measure head circumference before buying.
Building a Size-Smart Wardrobe
Here's how many items we recommend having in each size:
- Size 0000: 3-4 items only (many babies skip this size or wear it briefly)
- Size 000: 6-8 basic items plus 2-3 special pieces
- Size 00: 8-10 items (babies spend several months in this size)
- Size 0: 10-12 items (usually worn for 4-6 months)
- Size 1+: Build as you go based on growth rate
Focus on basics in smaller sizes and add more variety as your baby grows and you understand their size patterns better.
What To Do With Clothes That Don't Fit
Despite best efforts, you'll likely end up with some clothes that don't fit well. Options include:
- Return or exchange: If unworn with tags, return to the store
- Pass on: Gift to friends with babies or donate to charity
- Sell: Use marketplace apps or second-hand baby shops
- Store for future children: Keep if you plan to have more babies
Getting baby clothing sizes right takes some experience, but once you understand your baby's proportions and which brands fit them well, shopping becomes much easier. Remember that comfort matters more than perfect fit—your baby doesn't care if their sleepsuit is a little roomy, as long as they're happy and comfortable.