How to say "unbelievable" in Japanese

• すげーCommon
  interjection, expressionCovers 'unbelievable' as an exclamation of amazement at something impressive or astonishing; being colloquial, it suits casual talk with friends more than formal situations.
  うわっ？これ、勉強べんきょうに運動うんどう神経しんけい、全すべてのパラメータがMAXじゃないか！おまけにお金かねもカンストするまで貯たまってる・・・すげえ。↗

  Wha? Study, reflexes, all the parameters are MAX! You've even saved money up to the limit ... Amazing.
• 奇想天外きそうてんがいCommon
  na-adjective, no-adjectiveA four-character idiom covering 'unbelievable' in the sense of bizarrely inventive: ideas, schemes, or plots so outlandish they astound. It is not the everyday exclamation of surprise.
  このミステリーのトリックは、奇想天外きそうてんがいだ。↗

  This mystery has a plot twist that's completely novel.
• ありえないCommon
  i-adjectiveCovers 'unbelievable' in the sense of unthinkable or absurd — something so impossible it cannot be true. A natural reaction of disbelief, 'no way!', to something ridiculous; usually written in kana.

Choose 「すげー」 for casual spoken amazement at something impressive, 奇想天外 for ideas or schemes so bizarre they astound, and 「ありえない」 for disbelief at something absurd, ridiculous, or impossible.

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

• すげーincredible
• 奇想天外きそうてんがいfantastic
• ありえないほどunbelievable (extent)
• アンビリunbelievable
• アンビリーバブルunbelievable
• 信じがたいしんじがたいunbelievable
• とてつもないextravagant
• 嘘のよううそのようhard-to-believe
• 信じられないしんじられないincredible
• インクレディブルincredible
• 桁違いけたちがいan order of magnitude higher
• ありえないunthinkable
• 規格外きかくがいexceptional