Different file formats store data differently. Two main reasons for file size differences could be one format is most likely compressing out the blank/whitespace. The other reason is the file has some type of formatting. How much of a difference in size is based on the size of the Excel data. I ran a quick comparison 2,000 row by 26 columns in Excel. Size 147k Saved as MS-DOS TXT and it’s 228k.. Not big concern in difference.