Choosing the right shoe size when shopping online seems simple at first. A customer knows their size, selects it in an online store and expects the product to fit. In practice, EU 42 in one brand may feel different from EU 42 in another, and even two models from the same company can fit differently on the foot.
This is why shoe size charts are so important in footwear e-commerce. The problem is that they are not always identical. Differences between size charts come from many factors: measurement systems, shoe construction, model purpose, materials used and the manufacturer’s own sizing assumptions. Understanding these differences helps customers make better purchasing decisions and reduces the risk of returns.
To compare sizes between brands faster, you can use the shoe size converter on Sizetab.
A size chart does not always mean the same thing
The most common mistake is treating shoe size as a universal value. EU 40, US 9 or UK 7 does not guarantee the same fit in every brand. In practice, a size is only a label assigned by the manufacturer to a specific insole length, shoe last or recommended foot length range.
Some brands base their size chart on foot length, others on insole length, while others use their own conversion rules between EU, US, UK and CM systems. As a result, a customer may see the same size on the label but receive a shoe with slightly different length, width or internal volume.
That is why, when buying shoes online, it is worth looking not only at the size number itself, but above all at the values given in centimeters. CM length is often the best reference point, especially when comparing sizing between different manufacturers such as Nike, Adidas or New Balance.
Different brands use different shoe lasts
One of the most important reasons for sizing differences is the shoe last, which is the form used to design the shoe. It affects length, width, instep height, toe shape and the overall position of the foot inside the shoe.
A brand that produces sports shoes may use different lasts than a brand specializing in formal footwear. Even within sneakers, the differences can be clear. One company may design shoes that are more fitted and narrow, while another may focus on a looser, wider comfort fit.
This means that a person who wears EU 42 in one brand should not automatically choose EU 42 from another manufacturer. In some cases, a larger size will be better; in others, a smaller one. Sometimes the key factor is not length, but shoe width. Before buying, it is worth checking a specific comparison, such as Nike vs Adidas, New Balance vs Nike or Adidas vs New Balance.
The shoe model matters as much as the brand
Differences in size charts do not occur only between brands. They can also appear between models from the same company. This is because every type of footwear is designed for a different purpose.
Running shoes often provide more space in the toe area because the foot moves during activity and may swell slightly during exercise. Lifestyle sneakers may be more visually fitted to look better on the foot. Hiking shoes need to account for thicker socks and foot stability, while formal shoes often have a narrower toe box and a stiffer construction.
For this reason, two models from the same brand in the same size can feel completely different. One may be comfortable from the first wear, while the other may feel tight, even though the size chart shows the same size label.
Materials affect shoe fit
Another factor is the material. Shoes made from natural leather may slightly adapt to the foot over time. Footwear made from stiff synthetic materials usually keeps its original shape and stretches less. Models with an elastic upper may feel more forgiving in terms of sizing, while shoes with rigid panels require a more precise fit.
The inside construction of the shoe is also important. Thick lining, additional reinforcements, cushioned insoles or insulation can reduce the real space available for the foot. That is why winter shoes, highly cushioned sports shoes and technical models may require a different sizing approach than lightweight everyday shoes.
EU, US and UK systems do not convert perfectly
Size charts also differ because EU, US and UK sizing systems do not have one perfect conversion formula. A European shoe size does not always convert directly into a US or UK size. In addition, the US system differs for women, men and children.
This means that a simple conversion such as “EU 42 = US 9” may only be an approximation. For one manufacturer, EU 42 may correspond to US 8.5; for another, US 9; and in yet another chart, it may have a different CM value. These differences are especially important for stores serving international customers.
The safest approach is to compare several values at once: EU, US, UK and length in centimeters. You can use the EU, US, UK and CM shoe size converter to compare size labels used by different brands.
Why are size charts sometimes inaccurate?
Not every size chart is created with the same level of accuracy. Some stores use general charts intended to fit an entire product category. Others copy manufacturer data but do not account for a specific model. Sometimes a chart is accurate for one collection but not necessarily for newer or older versions of the product.
Another issue is the lack of distinction between foot length and insole length. Customers often do not know whether the CM value refers to recommended foot length or the physical length of the insole inside the shoe. This is an important difference because the insole should usually be slightly longer than the foot to provide comfortable extra space.
How to use size charts when buying shoes online
The best solution is to start by measuring your foot. The customer should measure both feet, preferably at the end of the day, and use the larger result as the reference point. Then it is worth comparing that result with the size chart of a specific brand, not just a general size chart.
It is also useful to check which size the customer wears in a brand that already fits well. This known reference point helps compare sizing with a new brand. If the user knows they wear EU 42 in Adidas, they can check the closest equivalent in Nike, New Balance, Vans or another brand.
Brand pages can help with this, such as the Adidas size chart, Nike size chart, Vans size chart and Puma size chart. They make it easier to compare CM, EU, US and UK values within a specific manufacturer.
What do size chart differences mean for online stores?
For e-commerce, differences in size charts are an important part of the shopping experience. A store that provides only a general size label leaves the customer with a lot of uncertainty. This can lead to abandoned carts, ordering several sizes at once and more returns.
A better solution is to present size charts at brand or model level, add CM length, explain how to measure feet and provide fit guidance. It is also worth informing customers whether a given model fits true to size, large, small, narrow or wide.
An online store can also link to a supporting external tool such as Sizetab, so the user can compare sizes between brands before placing an order. This type of support increases trust, reduces customer service questions and may lower the risk of returns.
FAQ: why do shoe sizes differ between brands?
Is EU 42 the same in every brand?
No. EU 42 may differ in insole length, width, last shape and overall fit. That is why before buying, it is worth checking the size chart of a specific brand or using a shoe size comparison between brands.
Which is more accurate: EU, US, UK or CM?
The CM value is usually the best reference point because it relates to foot length or insole length. However, you still need to check how a given brand interprets this value in its own chart.
Why can the same size in two models from one brand fit differently?
Models can have different purposes, construction, materials, toe shapes and cushioning levels. That is why a running shoe, lifestyle sneaker and hiking shoe in the same size may fit differently.
What is the best way to choose shoe size online?
First, measure your foot in centimeters, then compare the result with the size chart of a specific brand. If you are switching manufacturers, also check the online shoe size converter or a specific brand comparison.
Summary
Size charts differ by brand and model because manufacturers use different lasts, constructions, materials and conversion rules between sizing systems. The size number alone is not always enough to choose shoes correctly online.
The safest approach is to compare the size with length in centimeters, check the size chart of the specific brand and consider the type of footwear. For online stores, this means presenting sizing data more clearly, while for customers it means a better chance of choosing the right pair on the first attempt.