Get posts_per_page via API

Hello, I’m trying to create my own code with API example https://gist.github.com/ajaydsouza/c8defd4b46e53240e376 but API overall is not existing – at least I can’t find it after few hours of searching

But I can’t find any information how to gather information – option settings saved in admin panel as “Number of post to display” in “post list” tab

So I’d like to have posts_per_page information in php file coming from admin panel.

Thank you in advance