A lot of sites I read regularly, such as that of newspaper NRC, display reading times for each article. I have added the same functionality to the Word counter tool at https://www.reuneker.nl/files/wordcount, so you can get an indication of reading times for your own texts.
You can set an average of words per minutes (wpm), or just leave it at 250, which I find more realistic than what is considered the average for adults, i.e. approximately 300 words per minute (see Quantz, 1898). To read about why this average is debatable, see Brysbaert (2019).
Reading time calculation
I find it rather useful just to get an indication for presentation texts, script for voice-overs and such. I hope you'll find it useful too!