Kids Clothing Size Chart 2026: Why the Same Label Fits Differently at Every Brand

By Outgrow Research · Updated April 2026 · Based on verified measurements from 36+ official brand size charts

If you've ever bought size 6 from two different brands for the same child and had completely different results, you've discovered the central problem of children's clothing: there is no standard sizing system. Every brand sets its own measurements, and the gap between the most generous and most conservatively cut brands at the same label can be enormous.

This guide covers what we found when we verified the measurements behind 36+ brands and simulated 1,000 children across four age bands to establish which brands genuinely run generous or slim — and why the same label produces such different outcomes. The full simulation methodology is documented in Does Kids Clothing Run Big or Small?.

Find Your Child's Size Across All Brands at Once

Enter your child's height and we'll show the correct size for Carter's, Gap, Old Navy, H&M, Zara, M&S, Next and 30+ other brands — side by side, so you can see exactly why the sizes differ.

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Size recommendations are based on official brand size charts and are provided as a guide only. Fit may vary by item, style, and individual child. Outgrow is not responsible for sizing decisions made based on these recommendations.

The "Size 6" Problem

We verified the measurements behind every brand's "size 6" label — or closest equivalent — for boys tops across 16 major US brands. The results show that "size 6" spans a midpoint height range from 113cm at the smallest to 123cm at the largest. That is a 10cm difference between brands using the same label.

For a child at 118cm (approximately 46 inches), here is what "size 6" means at six major US brands:

Same label. Six completely different outcomes for the same child. This is why "Carter's runs small" and "H&M runs small" become internet truth — parents are comparing labels, not measurements. Carter's doesn't run small compared to Gap Kids. H&M doesn't run small compared to Old Navy. They just define the same label differently.

The fix is simple: always check the height bracket behind the label, not just the number or age on the tag.

Our Methodology

The findings in this guide come from two sources. First, direct verification of measurements from official brand size charts — every number in our database is checked against the brand's own published data. Second, a Monte Carlo simulation of 1,000 children across four age bands (baby 50–92cm, toddler 92–110cm, kids 108–140cm, older kids 138–165cm), using proportional interpolation within each size bracket to eliminate the bracket position bias that affects simple reference point comparisons.

The simulation cross-brand mean for chest is 0.0cm, waist −0.1cm, and hip +0.1cm — effectively zero, confirming the methodology is correctly normalised. Brands are flagged as generous or slim only when their deviation exceeds 1.0 standard deviation from the cross-brand mean, with confidence ratings based on data completeness. Full method: Does Kids Clothing Run Big or Small?

Which Brands Actually Run Generous or Slim?

The short answer is that most brands sit at the cross-brand average. The widespread belief that H&M runs small, Zara runs small, or George runs generous is not supported by the measurement data. These brands appear in parenting community discussions as outliers because parents are comparing labels rather than measurements.

The brands that do genuinely deviate from average are often surprising.

Brands that run genuinely generous (verified)

Brands that run genuinely slim (verified)

Cross-Brand Comparison at 112cm

Our reference child is 112cm tall with a 53.5cm waist and 58.5cm hip — the midpoint of the kids age band. Here is how the major brands compare for standard bottoms waist at this height:

UK brands at 112cm — boys standard bottoms waist

US brands at 112cm — boys standard bottoms waist

Sportswear brands (Nike, Under Armour) run generous in the waist at this height — consistent with performance wear designed for movement. Fashion brands (H&M, Zara, Next, Primark, George) all cluster tightly around the average. M&S boys stands dramatically apart from every other UK brand.

US vs UK vs European Sizing: The Key Differences

The most important structural difference between US and European kids clothing is not the cut — it's how the size label is constructed.

US brands (Carter's, Gap Kids, Old Navy, Target) use age-based T-sizing (2T, 3T, 4T) for toddlers transitioning to numeric sizes (4, 5, 6, 7) for older children. The age label is a rough guide and brands are reasonably consistent with each other within the US market.

UK and European brands (H&M, Zara, Next, Primark, M&S) primarily use height in centimetres as the size indicator, with age as a secondary guide. H&M size 116 means the garment is designed for a child up to 116cm — the number is the upper height limit, not a midpoint. This creates immediate confusion for parents used to US age-label sizing.

The practical implication: When buying across US and UK brands for the same child, use height as the common currency. A child at 110cm fits H&M 110-116 and Carter's 5 and Next 4-5 — three different labels, similar height brackets. Always verify the height range behind the label rather than assuming the number corresponds to anything consistent.

What Does 4T vs Size 4 Mean?

4T is designed for toddlers who may still be in nappies — extra room in the seat, shorter rise. Size 4 is for potty-trained children with a slimmer seat and longer rise. They cover similar height ranges (approximately 98–107cm) but different proportions. Most children transition to numeric sizes around age 4–5, and switching to size 4 often provides a better fit for potty-trained children even if they were comfortable in 4T.

The same T-to-numeric transition occurs at each size — 2T vs 2, 3T vs 3. Some brands (Carter's, Gap) sell both for the transitional age range. Others (H&M, Next) don't use T-sizing at all.

How Long Do Kids Clothes Last?

Average wear times based on verified growth rate data across age bands:

These are averages. Children in growth spurts can outgrow a size in half the typical time. The only accurate predictor for a specific child is tracking their individual growth rate — which is what Kids Size Finder does automatically between measurements.

Brand-by-Brand Size Guides

We've published complete verified size charts for each brand below, covering baby through teen sizing, how the brand compares to others at the same height, and simulation findings where available.

US Brands

UK Brands

International Brands

How to Measure Your Child

• Height — stand your child against a flat wall without shoes, feet together, looking straight ahead. Mark the top of the head and measure from the floor. This is the most important measurement for finding the right size at any brand.
• Weight — useful for baby and toddler sizes where build varies significantly at the same height. A morning weight on a digital scale is accurate enough.
• Chest — measure around the fullest part of the chest, tape horizontal and snug, arms relaxed at sides. Important for tops at brands that publish chest data.
• Waist — measure at the natural waist, just above the belly button. Snug but with room to breathe. The most important measurement for choosing between standard and extended fits (Slim, Husky, Plus).
• Hip — measure around the fullest part of the hips and bottom, tape horizontal. Published by most brands for girls bottoms, fewer for boys.
• Foot length — place your child's foot on paper, mark heel and longest toe, measure the distance standing. Always measure both feet and use the larger. More reliable than shoe size conversions between brands.

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