How to say "king-size" in Japanese

• 特大とくだいCommon
  no-adjective, na-adjectiveThe common, everyday choice: it treats king-size as simply extra-large, marking something bigger than the largest regular size, as on food packaging or menus.
  特大とくだいのサイズはあるんですが、その色いろのは切きらしております。↗

  We have the extra-large size, but not in that color.
• キングサイズ
  no-adjectiveThe straight phonetic borrowing of the English term; less common than 特大, it appears where the English size name itself is used, above all for bed and mattress sizes.

Choose the common 特大 when king-size just means extra-large — something bigger than the largest regular size; the loanword 「キングサイズ」, less common, turns up mainly where English size names are kept, as with bed sizes.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 特大とくだいextra-large
• キングサイズking-size