yii\validators\FileValidator::sizeToBytes PHP Method

    private function sizeToBytes($sizeStr)
    {
        switch (substr($sizeStr, -1)) {
            case 'M':
            case 'm':
                return (int) $sizeStr * 1048576;
            case 'K':
            case 'k':
                return (int) $sizeStr * 1024;
            case 'G':
            case 'g':
                return (int) $sizeStr * 1073741824;
            default:
                return (int) $sizeStr;
        }
    }