C# - Format a file size

Here's how you can format a file size, specified in bytes, into a nice string for display:

public const string DECIMAL_FORMAT = "0.##";
public static string ToFormattedSize(int size) {
  float KB = 1024f;
  float MB = 1024f * KB;
  float GB = 1024f * MB;

  if (!size.HasValue)
    return "-";
  else if ((float)size.Value > GB)
    return ((float)size.Value / GB).ToString(DECIMAL_FORMAT) + " GB";
  else if ((float)size.Value > MB)
    return ((float)size.Value / MB).ToString(DECIMAL_FORMAT) + " MB";
  else if ((float)size.Value > KB)
    return ((float)size.Value / KB).ToString(DECIMAL_FORMAT) + " KB";
  else
    return ((float)size).Value.ToString(DECIMAL_FORMAT) + " B";
}