There's really no standard keyword density. Most SEOs say 1-5% but 5% is a little on the high side. I personally only stick to 1-2% and only use them naturally and it's been working like a charm. Above all else, just don't keyword stuff.
I personally think this isn't worth paying attention to. Focus on good content that serves the interest of your readers. Use keywords where they make sense. Your time can be better spent focused on other things like promoting the content you write, writing more content, outreach, and growing your list.
In the past I have run a few reports on my own site and the ideal keyword density appears to be between 2-4% so that fits in with what the user above indicates. Totally support the statement.
Specific keyword density recommendations are a thing of the past, not SEO 2014. Today the key is to write naturally. Read your copy out loud to yourself. If it sounds stilted, contrived, "SEO-ish," rewrite it! If it sounds good to your ear, that's what you are looking for. Keep that up. And just use multiple words, phrases, and synonyms in your copy to describe your main point(s). If the copy read aloud sounds good, go with it.
I think this is depend on the content length and quality of content. if our content is unique and fresh having 1500 characters. then we must use 2-4% keywords in our article.
It's not as simple as saying "use your KW x times" as it depends of the lenght of the articles. Don't worry much about that, search for LSI and topic related keywords and use them on your content and write for the people, not for search engines.
Ever since the hummingbird update and the increasing database that google uses for semantic index and synonyms, keyword density is useless. It's outdated and if you try to optimize your content using older methods like 5% keyword density etc.. you actually increase your risk of getting penalized.