No formula is needed if you set up a summary report with a sub summary layout part.
Define a summary field as the total of your size field.
On a list view layout, use part setup to add a sub summary layout part "when sorted by your program field".
Put the summary field in this layout part and be sure to sort your records by program and you will get one sub total for each program. You can show all records to get these sub totals for all your records in the table or you can perform a find to see sub totals based on a sub set of all the records in your table.
If you only want sub totals and not the individual records listed, remove the body layout part from the layout. Note that if your records are not sorted by program and you remove the body layout part, your layout will appear empty until you sort the records.