By default, Recycle Bin can occupy up to 10 percent of your hard disk space, which means it has files so old you can't remember them. To determine a reasonable size, open it and click twice on the Date Deleted button to sort the deleted-files list in reverse chronological order. Scroll down to the first file that's more than a month old. Select it, then scroll to the bottom of the list. Hold down the Shift key and select the last file, thereby highlighting all files older than one month. Press the Delete key to permanently remove them. Now open Explorer and highlight the Recycle Bin icon. Note the amount of space occupied by the remaining files, as reported on the Status Bar at the bottom of the window. That's how much space your Recycle Bin really needs to hold one month's worth of discarded files.  Convert it to a percentage of your total drive space, then move the Recycle Bin's Maximum size slider to that value.