How can I find out which parts of an Excel workbook are the biggest in size?

Didn't mean to answer my own question but I found out how to do it afterwards. So here's the deal:

1. First, make a copy of the file, rename it as .zip, open it and navigate to [zipfile]\xl\worksheets\ There you'll see the .xml files with their uncompressed size. For instance:

2. Identify the biggest worksheet, in this case sheet6.xml

3. Open the file [zipfile]\xl\_rels\workbook.xml.rels and find out the corresponding relationship id of the previously identified worksheet.xml. In this case the r:id of sheet6.xml is 10:

4. Open the file [zipfile]\xl\workbook.xml. Using the rid of the big .xml file you got above and the structure of workbook.xml (shown below), find out the name of the big sheet in your workbook.

I am unable to Comment (not enough points) but I used this in addition to the Awesome answer provided by S_A to get my bloated file from 75mb down to 1.7mb...

I had NEVER heard of the "Clean Excess Cell Formatting" feature before... (BTW, it's part of Excel, not a 3rd-party product...)

Sorry for submitting this as an answer, but I wanted to tell you about this helpful tool, and thank you for your helpful discussion! Hoping to get enough points someday to participate...

Edit: at the recommendation of robinCTS, I'm going to quickly show how to enable/access this tool from within Excel