PHP | Function | Convert UK shoe size to EU

uk_to_eu_shoe.php

<?php
// Convert UK shoe size to European size
function euro_shoe( $uk_size ) {
    $eu_size = null;
    if( ! is_numeric( $uk_size ) ) {
        return $eu_size; // Abort if we are NOT dealing with a number
    }
    if ( in_array($uk_size, range(2, 19, 0.5)) ) {
        // Check to make sure it is a sensible shoe size number using a range with half size steps
        // Now work through the equation 
        $eu_size = $uk_size + 23;
        $eu_size = 1.27 * $eu_size;
        $eu_size = $eu_size + 2;
        $eu_size = round($eu_size); // Lets round to whole number
    }
    return $eu_size;
}