One of the lecturers in our university is not a native English speaker (as I am not as well) and he asked

How much time do we need for such an experiment?

I know that the correct way is: "How long ..." or "How long time do we need for such an experiment?"

  • My question is whether or not it's a mistake to say "How much time"?

2 Answers 2


"How much time" and "how long" can be used in place of one another in many common situations. In the situation you describe, both would sound natural and be correct grammar.

"How long time" is always a mistake. It is not correct grammar under any normal circumstance.

  • Thank you. so if for example I'm saying to my girlfriend (which flied for two weeks to visit her parents) "how long time I will wait you", is it a mistake? and which form will you use for this context? Sep 26, 2016 at 23:30
  • 2
    @Assiduous If you know how long your girlfriend is going to be gone, why would you need to know either how long or how much time? If you want to express sadness at the separation, you might write something like What a long time to wait before I see you again!
    – choster
    Sep 26, 2016 at 23:38
  • "How long time" is always a mistake. "How long" already includes the idea of "time" inside of it. In this situation "How long will I wait for you" is the normal way to say it. Unfortunately, I don't think I can really explain when to use which one out of "how long" and "how much time". It's very much based on intuition, but one simple rule to start with is that if the period of time is more than a few hours, "how long" is much more likely to sound correct.
    – leoger
    Sep 26, 2016 at 23:42
  • @choster, good catch. Assiduous, it depends if you are asking a question because you don't know how long or if you are trying to communicate something like "Two weeks is a very long time! I will miss you!"
    – leoger
    Sep 26, 2016 at 23:46
  • Yes, both of you mentioned true things. So If I don't know for how long she will be there and when she is coming, then it would be correct to say "how much time can I wait for you"? Sep 27, 2016 at 0:14

Your lecturer is better than you think:

  • How much time do we need for such an experiment?
  • How long will it take to complete such an experiment?

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