Sum up the users? Or sum up the number of users?

Let's say that there is a list of users and I want to know how many users are in the list.

Would I 'sum up the users,' 'sum the users,' 'sum up the number of the users,' 'sum the number of users,' or something else?

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None of those; you would count the users. – jwpat7 Jan 10 '13 at 23:56
I am not looking for writing advice, per se. This is a question about grammar, right? I want to know the proper was to use the word 'sum.' – Chris Morris Jan 11 '13 at 17:26
Or a question about 'word choice/usage,' which is a valid topic. – Chris Morris Jan 11 '13 at 17:27
I would argue that "sum" isn't the right word there anyway, you want to count the number of users. But I don't think that's really your question, right? – bmearns Jan 11 '13 at 17:38
This question is not appropriate for the Writers site. The OP is asking for clarification on the usage of a phrasal verb, which is clearly in EL&U's bailiwick. – Kit Z. Fox Jan 13 '13 at 1:06

You would "sum up the number of users." Or "sum the number of users." The verb "sum" applies to numbers so I think that the word "number" is needed in the sentence. The result would then be "the sum of all the users."

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'the sum of all the users' seems a little odd. Aren't there a lot of things that you could sum up about the users? How about the 'number of users'? – Chris Morris Jan 12 '13 at 19:28
No, it is correct. Yours is also though. – cbbcbail Jan 12 '13 at 21:42

To sum up a person, or a group, is to take their measure. It is not to count them.

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It's not wrong to use sum the way you intend, but if the method by which you reach the total amount of users in the list involves going through the full list, it is probably better to use the word count. On the other hand, let's say the users are divided into groups and you know the number of users in each group. Then you would definitely "sum the number of users in each group" to figure out the total amount of users.

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The word tally as a verb can mean

1. to count or reckon up.

This will encompass both the counting of individuals and the addition of the numbers of users identified in sub-groups.

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In your context, "summing up" really means "giving a summary."

Summing up the users, we find six of them chose Kirk, four chose Picard, and two said they'd get us an answer on Tuesday.

If you just want to talk about the total number of users, you'd say:

The sum total of users was 12, all of whom were devoted Trekkies.

You would not use the verb "summing" without "up" in this context. "Sum" in "Sum total" is an adjective.

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What about saying 'the number of users was 12' or 'there were 12 users'? – Chris Morris Jan 12 '13 at 19:32
@ChrisMorris regarding that, you may find this useful: english.stackexchange.com/questions/43700/… – user19341 Jan 13 '13 at 14:40