One of the most exciting things about preparing for a new baby is filling their wardrobe with adorable little outfits. But working out which size baby clothes you actually need - and when - is a whole different challenge. Babies grow at lightning speed, and sizing can sometimes feel more like guesswork than guidance.
Whether you're prepping your hospital bag or shopping for your toddler’s next wardrobe refresh, this baby size guide will help you confidently choose the right clothes at every stage. From 0-3 months to 18-24 months, here's what to expect - and what to buy.
Understanding Baby Clothing Sizes
Baby clothes are usually sized by age, but every little one grows at their own pace. That’s why it’s helpful to think of the size labels as a rough guide rather than an exact fit. Some babies may grow out of newborn sizes before they even leave the hospital, while others might stay snug in 0–3 months for a little while longer.
To help make things easier, we’ve broken down our baby clothing by age ranges so you can shop confidently:
What to Buy at Each Stage
Newborn & Tiny Baby Sizes: For the Very Early Days
While many parents start with 0–3 month sizes, it’s worth noting that some babies - especially those born early or on the smaller side - may need something more petite. Our Tiny Baby Clothes are specially designed to fit babies weighing up to 7lbs, with soft, gentle fabrics and fuss-free fastenings ideal for their first days.
For babies born full term, Newborn Baby Clothes offer a perfect first fit, designed to be comfortable, breathable, and easy to change during those round-the-clock feeds and nappy changes.
0–3 Months: The Newborn Essentials
In many cases this size is perfect for your baby’s early weeks. Opt for soft sleepsuits, bodysuits and easy-dressing styles with front poppers. Keep layering in mind - babies can’t regulate their temperature, so breathable cotton is your best friend.
Top Tip: Buy a few pieces in 0-3 months, but don’t overstock - your baby may outgrow them quickly!
3–6 Months: Starting to Stretch
By this stage, your baby will likely be more active, with lots of wriggling and kicking. Choose clothing with a bit more stretch and room to grow. Multipacks of basics will go a long way.
Look for: Expandable necklines, footless rompers, and layering cardigans.
6–9 Months: Sitting Up & Exploring
As your baby starts sitting, rolling and becoming more mobile, go for comfy clothes that move with them. Reinforced knees or thicker materials are a great shout for tummy time adventures.
Must-haves: Soft joggers, long-sleeve tops, and cosy knitwear.
9–12 Months: Crawling & Climbing
Mobility is really taking off now! Practicality is key - think separates, easy fastenings, and outfits that hold up to lots of movement (and mess!).
Don't forget: Bibs and spare changes are essential during this stage of exploration.
12–18 Months: First Steps
Walking means even more action. Look for non-slip soles on sleepsuits and clothes designed to support movement. This is also a great time to introduce more playful styles.
Shop for: Leggings, roomy tops, and transitional outerwear.
18–24 Months: Growing Independence
Your little one is likely trying to dress themselves now, so choose simple designs with elasticated waistbands and big buttons. Their personality is shining through - let their clothes match!
Popular picks: Mix-and-match outfits, soft dungarees, and easy t-shirts.
Buying Ahead & Dressing for the Weather
It’s tempting to stock up on baby clothes in advance - especially when there’s a tempting bundle or seasonal sale. But buying ahead does take a bit of forward planning, especially when you factor in how quickly babies grow and how the weather might change by the time they fit into a certain size.
Here’s how to think seasonally when planning your baby’s wardrobe:
Spring
Summer
Autumn
Winter
Planning tip: If your baby will be in a car seat frequently, avoid thick coats and layer instead with blankets for safety.
General Rule: Babies grow fast. It’s wise to have a few basics in the next size up, but avoid going overboard - especially with seasonal styles they might outgrow before the weather turns. Stick with versatile pieces and build around the essentials as needed.
Final Thoughts
Understanding baby clothing sizes can feel like a minefield - but with this guide, you’ll be ready to shop smarter, dress easier, and enjoy every adorable outfit along the way.
Explore our full Baby Clothing by Age collection to find styles that suit every stage of your baby’s journey.
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