web/_includes/read-time.html

<!--
  Calculate the post's reading time, and display the word count in tooltip
 -->
{% assign words = include.content | strip_html | number_of_words: "auto" %}

<!-- words per minute  -->
{% assign wpm = 180 %}
{% assign min_time = 1 %}

{% assign read_time = words | divided_by: wpm %}

{% unless read_time > 0 %}
  {% assign read_time = min_time %}
{% endunless %}

<!-- return element -->
<span class="readtime" data-toggle="tooltip" data-placement="bottom" title="{{ words }} words">
  {{- read_time -}}{{" "}}{{- site.data.label.read_time_unit | default: "min" -}}
</span>