Estimating articles reading time
Based on the analysis of 190 studies, the average silent reading rate for adults in English is 238 words per minute for non-fiction and 260 words per minute for fiction. The difference can be predicted by taking into account the length of the words, with longer words in non-fiction than in fiction.
Mentioning the estimated reading time of articles seems to have positive impacts - it can reduce bounce rates and increase time spent on site. Letting your readers know how much time it takes to read your content improves user experience.
Calculating estimated reading time
The formula to calculate the average reading time is quite forward having the numbers described above:
Get the count of words in your article.
Divide that number by average words per minute.
Result's integer part represents minutes and decimal part the proportion of seconds (can be rounded up).
The decimal part, if you not rounded up, can be converted to seconds multiplying by 0.60.
Let's see an example:
We have 1000 words in a hypothetical article.
1000 / 238 = 4.20... (rounding with 2 decimals).
That means 4 minutes plus 1 minute if we round up the decimal part.
For greater precision, the decimal part can be converted to seconds: 0.20 * 0.60 = 12 seconds. That means 4 minutes and 12 seconds.
Keep in mind that while 238 words per minute is the average, this number may have to be adjusted depending on your article and audience. Besides, you should take into consideration other elements available in your article: inline images, schemas, tables, etc... A simple solution can be adding a predefined amount of seconds for each element type.