What should be the ideal length of a blog post?

There's no "standard" length. It depends on the topic. But regardless, always try to summarize. Some people don't have the patience to read and always skip contents that are too long. Choose words that resume the idea you want to deliver without having to explain and going into details.

The length is an important parameter in a blog. It should not be so long and too short. 400- 600 words is a good length. try to use perfect words. 

But the length also depends on the topic of blog. Science and fiction blogs can be longer.

500 words maximum and 250 words minimumPeople who read blogs are looking for content that is easily accessible and readable; the shorter the better.

A blog should be stating your point of view about a particular scenario or topic. The topic can be anything and that will decide the length of your blog. However, you need to keep in mind that you are not writing a dissertation and so your ideas and notions should be precise and subtle at the same time. This will help other bloggers to understand your way of analyzing the particular situation or scenario that you've blogged about and will also help you in being precise about whatever you think about.

300 to 500 words. But longer blogs (1000 to 2000 words) with the right keywords have the potential to rank highly in search engines. So make sure you put great attention to keywords and topic (niche)

This depends on the type of blog. But the post which is going to be upload should not be like an essay or story. but, post should be brief enough so that the reader not be boredoff. Use paragraph techniques and highlight or bold the curious words. In my opinion 100 t0150 words are enough.