size
Returns the number of characters in a string or the number of items in an array.
Input
{{ "Ground control to Major Tom." | size }}
Output
28
Input
{% assign my_array = "apples, oranges, peaches, plums" | split: ", " %}
{{ my_array.size }}
Output
4
You can use size with dot notation when you need to use the filter inside a tag:
{% if site.pages.size > 10 %}
This is a big website!
{% endif %}