<?php

function skill($val) {
    $val = trim($val);
    $last = strtolower($val[strlen($val)-1]);
    $val = (int)$val;
    switch($last) {
        case 'g':
            $val *= 1024;
        case 'm':
            $val *= 1024;
        case 'k':
            $val *= 1024;
    }
    return $val;
}

var_dump([skill("1M"), skill("2G")]);