Say you have a shoe store and you sell shoes across many different brands. Each brand has its own country of origin, and thus its own sizing standard. We have shoe brands with US sizing, other brands with UK sizes, other brands with IT sizes, and so forth.

What would be the best acceptable way to prompt a user on a product collection screen to filter by size? All customers are in the US, and it's assumed most customers wouldn't know their non-US standard shoe sizing.

Do we present multiple filter areas, each one containing its own standard and set of sizes (eg: "Filter by US Size" box, "Filter by UK size box", etc)? I see a potential challenge here with consumers not knowing what their foreign standard sizing would be.

Or do we combine filters to just "Filter by size" and display sizes in a combined format (eg: "US 3, US 3.5, ..., US 12, UK 3, UK 3.5, UK 4, ..., UK 12, IT 36, IT 36.5, ..., IT 49, etc)? I see the problem here similar to the above, but also users completely missing the fact that there are other sizing standards going on.

Or is there another solution?

Also, with a proposed solution, what is the best way to ensure engagement and visibility across shoes of a similar size but in a different sizing standard?

One line of thought would be in example A above, we create a mapping between standards so that when an option is chosen in one filter box, the related sizes are automatically selected in other sizing standard filters.

This one is really throwing us for a loop as to the best way to present and handle this crucial interactive component. We are also up against similar challenges in other departments, such as clothing and so forth.

  • One size filter. Each item has AT LEAST the US size. And if there's some other size standard put it AFTER the US size. Simply put, always a US size, and first. Nov 17, 2022 at 11:21
  • "I see the problem here similar to the above, but also users completely missing the fact that there are other sizing standards going on." Please elaborate. Nov 17, 2022 at 11:22
  • @bloodyKnuckles thanks for the comment. To elaborate, in your example, if we're listing US size first followed by other sizes, and a user clicks a US size, should we automatically select other size standards that match the selected US size? The selection for shoes with US sizes could only be 1/3 of the catalog, while the remaining 2/3 could be in another sizing standard.
    – Rob W
    Nov 17, 2022 at 13:08

1 Answer 1


For US customers the filter ought to be only US sizes.

And when filtering, automatically select foreign standard sizes that are compatible with the selected US sizes in the search results.

shoe filter

But when displaying the results, when applicable, show both the US and the foreign standard size for each item in the list.

If the first item in the results is a UK shoe include the UK size but show the US size also.

If the second item is a US shoe just show the US size.

shoe size zoom

It's important customers know, when they purchase a foreign made shoe, it is made to a foreign shoe size...no surprises when they first examine the shoes. But they always needs reassurance it fits and this can only be accomplished providing the comparable US size. For those two reasons, put the US size first (assurance), in parenthesis (translation), and followed by the country of origin shoe size standard, i.e., the size marked in the shoe.

Layout credit goes to 6pm.com

  • This is a great idea. Question, in the size selection box on the left, would we have multiple grouped boxes (one for each size standard), or combine all sizes into one box? If the latter, do we group up sizes by standard, or group up sizes by size?
    – Rob W
    Nov 17, 2022 at 20:15
  • 1
    @RobW My suggestion is ONLY US sizes in the filter box. No foreign standards in the filter box. When people talk in terms of Celcius, metric, foreign currency, speak foreign languages... it's meaningless. Speak your customers' language, and that's US shoe size. — I DO recommend putting the foreign shoe size for the foreign shoes so people know they're getting a UK 6, but first put the US compatible size, in parenthesis, so they know if fits. Nov 17, 2022 at 22:07
  • I'm with @bloodyKnuckles on this one. Don't increase the complexity for just a small % of users. Make it easier: consider providing a link or button to a popup/modal with a sizing guide right under the size filter. Here the user can quickly check what their size is in a different standard, and remember that when looking at more shoes. They don't have to know or see all the different sizes, they're not all relevant to them. Nov 18, 2022 at 8:11
  • Example: My EU size is 44, so if I'm on a US site that uses the US size standard, I could use the guide to see that my size in US standard is 10 or 10.5, so I can use that to continue browsing through shoes. Nov 18, 2022 at 8:14
  • Just ran across a site called cettire that has a really nice filtering/sorting for sizes. This looks like an interesting user pattern that we may also need to test. Thank you for your input!
    – Rob W
    Nov 21, 2022 at 15:09

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