When do you need to use the number of or the amount of with a noun? For example,

"If people go to gyms more, they will increase their physical activity."
"If people go to gyms more, they will increase their amount of physical activity."

"The number of CO2 emissions dropped last year."
"CO2 emissions dropped last year."

Is there a difference? Is one more correct than the other? Are there other contexts where the number of or the amount of must be used?

  • 1
    Well, you wouldn't say "... will increase the number of physical activity." But it would probably be better to say "The quantity of CO2 emissions dropped".
    – Hot Licks
    Mar 2, 2019 at 2:37
  • I can understand that it's not possible to say 'the number of physical activity' because this kind of activity is not countable, but can I say 'increase physical activity' - is this more or less correct?
    – Sam Varley
    Mar 3, 2019 at 11:27
  • "Increase physical activity" makes perfect sense, and is interesting because one could increase the rate or the duration, and probably still meet the condition of increasing.
    – Hack Saw
    Mar 7, 2019 at 17:17
  • Ah, I think I understand the difference a bit better now - and the point you made in your answer. So if you 'increase physical activity', this is ambiguous because it could mean the rate or duration or something else. - Thanks very much :) - I vote this comment as useful.
    – Sam Varley
    Mar 9, 2019 at 2:32

1 Answer 1


One would use "the amount of" when there is more than one property one could change. For instance, "If the duration of massage sessions produce diminishing returns, increase the number of sessions per month."

Note that the semantic difference here is that sessions are discrete events. One could talk about the rate of sessions, but for many people "the number" feels more correct when the things in question only come in whole units.

  • 2
    Agreed that massage sessions are discreet events, but more relevantly, perhaps, they are also discrete events.
    – remarkl
    Mar 2, 2019 at 5:27
  • I can agree that where there are whole units such as 'sessions' or 'lessons', then 'the number of' should be used. What about 'emissions' or 'physical activity' then?
    – Sam Varley
    Mar 3, 2019 at 11:26
  • Most people would regard those as continuous. One could speak of a number or emission sources, or a number of physical activities.
    – Hack Saw
    Mar 7, 2019 at 17:16
  • @remarkl: Ah, yes. Thank you for you discretion. :)
    – Hack Saw
    Mar 7, 2019 at 17:20
  • @HackSaw - thank you for your help :) . I think this answers the question.
    – Sam Varley
    Mar 9, 2019 at 2:35

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