A simple function to calculate the estimate reading time of a Wordpress post (article or page or custom post). Easy to use inside the loop code.

wordpress-time-to-read.php

<?php

/**
* Return the string with infos
* about the reading time of the post
*
* @return String computed reading time
*
* @author Andrea Rufo <www.andrearufo.it>
* @version 20210122
* @link https://www.andrearufo.it/2020/05/05/creare-una-funzione-per-il-tempo-di-lettura-di-un-articolo-di-wordpress/
*/
function get_readingtime(){

	// assumed 265 words per minute
	$words_per_minute = 265;

	// initialize the content
	$content = [];

	// the article title
	$content[] = get_the_title();

	// the article content
	$content[] = get_the_content();

	// all the contents
	$content = implode(' ', $content);

	// count the words inside the content
	$words = str_word_count($content);

	// count the seconds for the content
	$time = $words / $words_per_minute * 60;

	// add the time for 'read' the featured image
	if( has_post_thumbnail() ){
		$time = $time + 12;
	}

	// formatting the time
	$ii = intdiv($time, 60);
	$ss = $time % 60;
	$duration = $ii.':'.$ss;
	
	// a most readable format
	$timetoread = human_readable_duration($duration);
	
	// Ex. '2 minutes, 52 seconds'
	return $timetoread;
}