Japanese For Busy People volume II, revised third edition, on page 23 has

To state or ask how much bigger, you use other words.
Do you have one that is a size bigger?

However, the word (as of today) doesn't exist on forvo.com, on jisho.org (either as a word or in its corpora), the English or Japanese editions of Wiktionary, and on weblio it's only mentioned in sentences.

Is ワンサイズ a valid Japanese word, in that it's easily understood, unambiguous, and the most common way of expressing the concept of a difference of one size?

The only explanation I can think of as to why it's valid but not in dictionaries is that it's merely regarded as a combination of the words "ワン" and "サイズ".

  • @downvoter - what more research should I have done?
    – Golden Cuy
    Mar 6, 2018 at 9:45

1 Answer 1


Yes it's perfectly valid as a Japanese expression and is understood by virtually everyone (except for very old people). ALC has several examples of ワンサイズ. Although uncommon, you can say ツーサイズ, too. A non-katakana equivalent would be 一段階.

  • 3
    As an aside, スリーサイズ usually refers to something totally different, "bust/waist/hip measurements." :)
    – naruto
    Mar 6, 2018 at 14:25

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