Why Do Kids Clothing Sizes Differ Between Brands?

Hand holding children's clothing size labels showing ages from 3M to 6-7Y

If you've ever bought a "size 4" from two different brands and found that one fits your child perfectly while the other is too small — you're not imagining things, and you're definitely not alone. Children's clothing sizes genuinely vary between brands, and once you understand why, shopping gets a lot less frustrating.

There are three main reasons.

Different sizing systems

The world uses several systems for children's clothing. EU sizing is based on height in centimetres. US sizing uses age labels (2T, 3T, 4, 5, 6X). UK sizing uses age ranges (2–3Y, 3–4Y). French and Italian sizing uses centimetres similar to EU but not always identical. Each system has its own scale, so a "4" in US is not the same garment as a UK "4Y" or an EU "104" — even if all three technically target the same age group.

Brands build their own fit on top of the system

Even within the same sizing system, brands make their own decisions about how much room to add beyond the body measurement. This extra space is called "ease." A brand focused on outdoor and active wear might add more room in the shoulders and chest. A brand with a fashion-forward aesthetic might cut closer to the body. Both might label their garment "EU 104," but they'll feel completely different on the same child.

Garment type changes everything

Even within the same brand, different types of clothing behave differently. Jersey t-shirts and leggings are stretchy and tend to follow the label closely. Structured items like coats and denim often run smaller in the body. Swimwear is cut to fit snugly. In some markets, sleepwear is deliberately sized smaller for safety reasons.

What this means practically: the brand label and the age label are both just starting points. The most reliable thing you can do is use your child's height measurement as your anchor, then check the brand-specific size guide before ordering. Our brand comparison table on the LittleSizes homepage shows how Zara, H&M, Next, and Boden sizing maps to EU height measurements — so you can find the right size across multiple brands in one place.