The length of an article summary will depend on the length of the article you are writing about.
If the article is long (say, 10-12 pages) then your summary should be about four pages. If the article is shorter, your summary should be about one to two pages. Sometimes, an article summary can be less than one page.
The length of a summary will also depend on the instructions you have been given. If you are writing a summary for yourself, it’s up to you how long or short it will be (but remember, a summary is supposed to be a short regurgitation of the information outline in an article). If you are writing a summary for a class assignment, the length should be specified.