Medium and many other sites have a calculation for how long it might take you to read that particular post. How is that calculated and is there a library to add that to any site?
I'd assume that they're taking a word count and then using a predefined number of words per minute to figure out approximately how long the article will take to read.
For example, https://medium.com/fragmented-musings/295cc75cd1fd has approximately 600 words and has an approximate reading time of 3 minutes. From this we can deduce that they're assuming that around 200 words can be read in a minute. By diving 600 by 200, we arrive at 3.
http://www.spreeder.com/ says:
"To train to read faster, you must first find your base rate. Your base rate is the speed that you can read a passage of text with full comprehension. We've defaulted to 300 wpm, showing one word at a time, which is about the average that works best for our users. Now, read that passage using spreeder at that base rate."
I wouldn't be surprised if Medium is calculating read time the same way. It's just aesthetically pleasing and somewhat useful.
For example, https://medium.com/fragmented-musings/295cc75cd1fd has approximately 600 words and has an approximate reading time of 3 minutes. From this we can deduce that they're assuming that around 200 words can be read in a minute. By diving 600 by 200, we arrive at 3.