We live in a age where everyone wants instant gratification. If you can not provide a reason to read on in the first few paragraphs, then chances are your reader will loose interest and move on to something that is more interesting to them.
The Internet is a huge place, with uncounted writing opportunities, so it is only natural to wonder just what the ideal length of an online article is. As a general rule online articles should be kept to an average length of 300 to 500 words, with some leeway for shorter or longer works depending on the topic.
Why 300 to 500 words? Quite simply because it is long enough to actually say something about the subject you are writing about, and brief enough that your reader can read it in just a few minutes. This is by no means a hard and fast rule, since online discussions have proven that even those who are writing articles for websites have a difference of opinion on how long an article should be. 250 to 11,000 words, less, more… It all focuses around one general rule. Write how much you need to write to inform the reader, no more.