This is a common question, and there are more than a few ways to answer it.
Conventional wisdom – based on observing the sites that seem to rank well in Google and the other major search engines – says that anything between 200 and 500 words is likely search-friendly. It helps if you have a couple of subheads or bullet points now and then, but that’s enough to share some information, include a few keywords, and generally leave your customer with a positive impression of your business.
Going a bit deeper, however, the best answer is that it really isn’t about any standard length at all… what matters most is that you are producing content that your ideal customer wants to find.
In some cases, that might be a few paragraphs about a topic like this one; and others, it could be an eight-page, in-depth piece explaining some feature of your industry. The same goes for videos, picture posts, and other types of content: it all just comes down to capturing the interest of your best customers.
Producing SEO articles that are too short or too long is obviously a good way to lose people, but don’t get so focused on lengths that you miss the forest for the trees. The point of SEO is to find customers, so put that focus first, and the rest will take care of itself.