What word can I say if I want to give approximate number?

What to say if I want to tell approximate number of something. What should I say? E.g.

I have (around/ about/ some) 5 books.

Is there a rule for number approximation?

Solution 1:

There are some alternatives, depending on the context, situation and use. I provided an example for each of them (taken from the NOAD):

• Circa (often preceding a date: built circa 1935);
• Approximately (there are approximately 24 children per classroom);
• Around (software costs would be around $1,500);
• About (reduced by about 5 percent);
• Roughly (this is a walk of roughly 13 miles);
• Something like (there were something like fifty applications);
• Of the order of (sales increases are of the order of 20%);
• More or less (more or less symmetrical).

So, in your case, I'd use approximately, about or something like (choose accordingly to your situation, i.e. formal vs informal, written vs oral, etc.)

Solution 2:

• About: fine.
• Around: fine, slightly informal with objects (discrete things). This is perhaps best used with larger numbers or hours / abstract quantities: it will begin around six o'clock.
• Roughly: fine, but you would probably not use this with lower numbers; it implies that you've made an estimate.
• Approximately: very formal; usually a shorter word is better.
• Some: very informal in this sense; usually inadvisable in writing.

Solution 3:

Purely commentary on what others have written:

If you're speaking informally, about and around are the best: - I have around 5 books. - I have about 5 books. (I can't think of any contexts to distinguish them; they feel pretty similar)

Roughly works too by it feels like the answer was meant o give an exact number but you just don't know.

Some has a jaunty (and therefore not common) feel. "There are some 500 live cobra in the with the stolen bank vault, said the henchman"

Approximately is more technical sounding (a more formal version of 'roughly').

Something like is nicely informal (colloquial and common)

Circa is very academic sounding and usually used with dates (anything else is very formal sounding).

Edit: I just heard on national news an announcer say "some 300 deaths", so I think our impression that 'some' is informal is totally wrong. It's not overly formal, just acceptable in news.