1. Open the workbook in Microsoft Excel.
2. Click on the "File" tab in the top left corner of the screen.
3. Click on "Info" in the left-hand menu.
4. Under "Related People", you will see the size of the workbook in MB.
5. Click on "Show All Properties" at the bottom of the page.
6. Under "Document Properties", click on "Advanced Properties".
7. Click on the "Statistics" tab.
8. Here, you will see the size of each worksheet within the workbook.

To reduce the size of the workbook, you can try the following:

1. Remove any unnecessary data or formatting from the workbook.
2. Use Excel's built-in tools to compress images and reduce file size.
3. Use formulas and functions that are more efficient and require less memory, such as
   Code:

   INDEX/MATCH

   instead of
   Code:

   VLOOKUP

   .
4. Split the workbook into smaller files if possible.
5. Save the workbook in a different file format, such as CSV or XLSB, which can reduce file size.