reading_time.php

<?php

/**
 * Calculates approximate reading time in minutes.
 *
 * @param (string) $str
 *   The string of words to calculate reading time on.
 * @param (int) $words_per_minute
 *   The words per minute to divide the time by. Defaults to 270.
 * @return (string)
 *   The reading time in minutes.
 */
function calculate_reading_time($str, $words_per_minute = 270) {
  $words = str_word_count(strip_tags($str));
  $words_per_second = $words_per_minute / 60;
  $reading_time_seconds = $words / $words_per_second;
  $reading_time_minutes = round($reading_time_seconds / 60);

  if ($reading_time_minutes > 0) {
    $reading_time = $reading_time_minutes . ' min';
  }
  else {
    $reading_time = 'Less than a minute';
  }

  return $reading_time;
}