I’ve recently added “Estimated Reading Time” on EditorsKit plugin and thought it’d be a good idea to post that here. I’m using 275 WPM and image calculation similar to what Medium is doing. Here’s how it works, let me know if anyone has comment or suggestions.
I’ve also added easy way to display the reading time on frontend via shortcode
[editorskit display="wordcount" before="Reading Time: " after=" min"]
EditorsKit is a free plugin that you can download here : https://wordpress.org/plugins/block-options/