Navigating the complex world of children's clothing sizes can feel like cracking a secret code, especially when encountering metric sizes like "120." As of late 2025, the size 120 is one of the most common measurements used by global retailers, particularly those based in Asia and Europe, and it represents a highly specific fit based on a child's vertical growth. Unlike the often-misleading age-based sizing (like 6T or Size 7), the number 120 is a direct, metric measurement, offering parents a far more reliable way to ensure a perfect fit for their growing child.

This comprehensive guide breaks down exactly what size 120 means, its precise conversion to US and UK sizing, and the exact body measurements you need to know. The short answer is that children’s clothing size 120 corresponds to a child's height of 120 centimeters, typically fitting a child between the ages of 5 and 7 years old, and generally converting to a US Size 6 or 6X in most American apparel brands.

The Complete Size 120 Conversion and Body Measurement Profile

The metric sizing system, where the number directly relates to the child’s height in centimeters (cm), is a universal standard that eliminates much of the guesswork associated with age-based labels. Size 120 is a key milestone size, bridging the gap between toddler and older children’s apparel. Understanding the exact dimensions is crucial for online shopping or buying from international brands.

Size 120 Quick Conversion Chart (US, UK, and Age)

The following chart provides a clear, up-to-date conversion for size 120 across major international sizing systems:

• Metric Size: 120 cm (The base measurement)
• Height Range: 115 cm – 125 cm (45.3 inches – 49.2 inches)
• Typical Age Range: 5 to 7 Years Old
• US Size Equivalent: Size 6 or Size 6X (Often listed as a transition size)
• UK Size Equivalent: Size 5–6 or Size 6–7
• European Size Equivalent (EU): Size 116–122

Detailed Body Measurements for Size 120 (Centimeters & Inches)

To achieve the best fit, especially when purchasing trousers, dresses, or outerwear, you should rely on more than just height. The size 120 garment is designed to accommodate the following average body measurements:

• Height: 120 cm (47.2 inches)
• Weight: 18 kg – 25 kg (40 lbs – 55 lbs)
• Chest Circumference: 64 cm – 68 cm (25 inches – 27 inches)
• Waist Circumference: 59 cm – 63 cm (23 inches – 25 inches)
• Hip Circumference: 67 cm – 71 cm (26 inches – 28 inches)
• Inseam Length: Approximately 50 cm (19.7 inches)
• Sleeve Length (from shoulder): Approximately 43 cm (17 inches)

Pro Tip: Always add 1 to 2 centimeters of ease to your child’s actual measurements, particularly for the chest and waist, to ensure comfort and room for movement. This is known as "wearing ease" and prevents clothing from being too restrictive.

Why the 120 cm Metric System is Superior to Age-Based Sizing

The size 120 system, prevalent in European and Asian markets, is a testament to the accuracy of metric sizing. This system, which is based on the child’s actual height, is generally considered more accurate and reliable than the age-based system (like 5T, 6, 7, etc.) used predominantly in the US, UK, and Australia.

The Problem with Age Labels

The primary issue with age-based sizing is the enormous variability in a child’s growth rate and body composition. A six-year-old child can vary significantly in height and weight compared to another six-year-old. For example, a child who is tall for their age might need a US Size 8, even if they are only 6 years old, while a smaller child might still fit into a Size 5. Age is a poor indicator of fit.

The 120 cm system, by contrast, focuses on the one non-negotiable measurement for clothing: the child's height. If your child is 120 cm tall, a size 120 garment is specifically designed to fit that vertical length, making the fit of sleeves, pant legs, and torso length far more predictable.

Understanding the US Size 6 vs. 6X/7 Confusion

When converting size 120 to US sizes, you will frequently see the equivalents of Size 6, Size 6X, or Size 7. This variation is where the confusion lies, and it's essential to know the difference:

• US Size 6: This is the standard size for a 6-year-old, generally fitting children around 114 cm to 119 cm (45 to 47 inches). A child who is exactly 120 cm tall may find a standard Size 6 slightly short in the arms or legs.
• US Size 6X or 7: For a child who is 120 cm tall, the US Size 6X (or sometimes a small Size 7) is often the perfect match. The "X" in 6X typically indicates an "extended" size, meaning the garment has the same width as a Size 6 but is longer in the torso, sleeves, and pant legs to accommodate the 120 cm height. This extended length makes it the truest US equivalent for the metric size 120.

Brand-Specific Sizing Nuances for 120 cm Apparel

Even within the metric system, different brands may have slight variations in their cutting and fit. This is often due to the target market's average body type (e.g., Asian brands versus European brands) or the type of clothing (e.g., slim-fit vs. relaxed-fit).

Key Brands and Their Size 120 Fit

When shopping from global retailers, keep these brand nuances in mind:

• Hanna Andersson: This US brand uses metric sizing and explicitly lists 120 cm as equivalent to their US Size 8 in some charts, indicating they size up their metric labels to match their generous US sizing. Always check their specific chart for their "Hanna Size."
• Bosideng/Asian Brands: Brands like Bosideng often use a dual-number system, such as "120/60," where 120 is the height (cm) and 60 is the bust/chest circumference (cm). This provides a more precise fit for a child’s girth.
• European Brands (e.g., Reima, OTTOBRE design): These brands strictly adhere to the metric system, with size 120 being precisely for a 120 cm child, and they often provide accompanying waist and hip measurements to ensure a proper European fit.
• Fast Fashion Retailers (e.g., Zara, H&M): These retailers often use a range, such as "116–122 cm," to cover the 120 cm measurement, which is a common practice to minimize the number of SKUs (Stock Keeping Units).

Essential Takeaways for Shopping Size 120

To confidently purchase size 120 clothing and avoid the hassle of returns, follow these updated best practices:

1. Measure Height First: Always start by measuring your child’s height in centimeters. If they are between 115 cm and 125 cm, size 120 is the correct starting point.
2. Check the Chest and Waist: Due to variations in body shape, compare your child’s chest (64–68 cm) and waist (59–63 cm) measurements against the brand’s specific size chart.
3. Size Up for Outerwear: For jackets, coats, and snow gear, consider sizing up to 130 to allow for layering and to ensure the garment lasts for a full season of growth.
4. Prioritize the Metric Label: When shopping internationally, ignore the estimated age and focus solely on the 120 cm label, as it is the most accurate indicator of fit.
5. Be Wary of US Conversions: Remember that a US Size 6X or a small Size 7 is the closest equivalent to a true 120 cm metric size, while a standard Size 6 may be too short.

By using the 120 cm measurement as your guide, you are adopting a globally recognized, height-based standard that is far more reliable than old-fashioned age estimates. This approach ensures your child’s clothes fit comfortably and last longer, making shopping for new apparel a much simpler task.