Adding Estimated Reading Time to WordPress.

functions.php

<?php

// For Plugin: https://tr.wordpress.org/plugins/reading-time-wp/

function reading_time($post_id) {
    // Words per minute
    $wpm = 150;
    $post_content = get_post_field('post_content', $post_id);
    $number_of_images = substr_count(strtolower($post_content), '<img ');
    $post_content = strip_shortcodes($post_content);
    $post_content = wp_strip_all_tags($post_content);
    $word_count = count(preg_split('/\s+/', $post_content));
    $reading_time = ceil($word_count / $wpm);

    // If the reading time is 0 then return it as < 1 instead of 0.
    if ($reading_time < 1) {
        $reading_time = __('less than one minute', 'text_domain');
    } elseif ($reading_time == 1) {
        $reading_time = sprintf(__('1 minute', 'text_domain'), $reading_time);
    } else {
        $reading_time = sprintf(__('%s minutes', 'text_domain'), $reading_time);
    }

    return $reading_time;
}

?>