Convert byte to KB MB GB

public static string ToKMGTByte(ulong bytes)
{
    var suffix = new[] { "B", "KB", "MB", "GB", "TB","PB" };

    int idx = 0;
    ulong rtn=bytes;
    while (idx<suffix.Length-1 && (bytes >>= 10) > 0)
    {
        rtn = bytes;
        idx++;
    }
    return string.Concat(rtn, suffix[idx]);
}

        public static string ConvertToReadbleFileSize(long size)
        {
            return size > 1000000 ?
                (Math.Round((double)(size / (1024 * 1024)), 2)).ToString("0.00 GB") :
                (Math.Round((double)(size / 1024), 2)).ToString("0.00 MB");
        }