Practice JLPTHow to tell them apart
だけ is the everyday word for limiting something to the extent or amount that applies, and it also carries the as-much-as reading in patterns like 伸びるだけ伸びた. のみ means only/just in a stricter, more formal way and does not carry the as-much-as reading, so swapping のみ into 伸びるのみ伸びた would be wrong. Choose のみ when the tone is written or formal and the point is simply this and nothing else.
- だけ Use だけ for everyday limits or the as-much-as pattern in casual and neutral speech.
- のみ Use のみ in formal or written contexts to state that something is exclusively one thing.
だけ dake
As much as/Only
As much as; as ~ as possible; as much as one wants | A particle meaning “to the extent that someone (can/wants to) do something or something can happen”.
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うちの子は背が伸びるだけ伸びた感じです。
It looks like my child has grown as much as he is going to.
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お金は使うだけ使っても故障の少ない車が買いたい。
I'd like to buy a trouble-free car no matter how much it costs.
のみ nomi
Only / just (formal)
Only; just; alone | A particle which expresses a limit imposed upon an action, event, or a state.
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この答えは私のみ（が）知っている。
Only I know the answer to this.
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これは吉田先生にのみ話してあります。
I have told this only to Professor Yoshida.
だけ and のみ are JLPT N5–N3 grammar points that Japanese learners often mix up. This page compares them side by side — meanings, usage and example sentences — so you can tell them apart.