regular expression for file size in asp.net?

   ErrorMessage="File size should not be greater than 1 KB." OnServerValidate="CustomValidator1_ServerValidate">

protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args)

    {

        if (fuFile.FileBytes.Length > 1024) // 1024*KB of file size

        {

            args.IsValid = false;

        }

        else

        {

            args.IsValid = true;       

        }

    }