Excel file size too large? How to find why and reduce it

A workbook that was 200 KB last year is 40 MB now and nobody knows why. The size is rarely the data. Here are the built-in fixes, where they stop, and one option that shows what the size is made of first.

Hullspark · updated 2026-10-29

Short answer

Save in binary format: File > Save As > Excel Binary Workbook (*.xlsb) [1]. It is a different file format, so check that everyone who opens the file can open it.
Pictures: Picture Format > Compress Pictures, or File > Options > Advanced > Image Size and Quality, default resolution 150 ppi or lower [1].
Pivot cache: PivotTable Analyze > Options > Data, clear Save source data with file [1].
Formatting on empty cells: formatting unused cells, especially whole rows and columns, can make a workbook grow quickly. The Inquire tab has a command for it in some editions [2].

What Excel gives you out of the box

Excel's built-in ways to reduce file size
Way	Good for	Catch
Excel Binary Workbook (.xlsb) [1]	One setting, no cleanup	A different format. The file is not .xlsx any more
Compress Pictures [1]	Photos pasted into sheets	Cropped areas and editing data can be deleted and not restored [1]
Do not save the pivot cache [1]	Workbooks with PivotTables	The PivotTable must be refreshed before use. Microsoft also says to tick Refresh data when opening the file [1]
Delete unused worksheets [1]	Old data nobody needs	You decide what is unused
Clean Excess Cell Formatting (Inquire tab) [2]	Formatting past the last used cell	Inquire tab, some editions only [2]

Doing it by hand

Copy the file first. Some of these steps cannot be undone.
Note the size. Then check where it comes from: many photos, PivotTables with a saved cache, or formatting that runs far below the data.
Press Ctrl+End. If the cursor lands far below or to the right of your data, the sheet remembers cells you no longer use.
Compress the pictures and set the default resolution to 150 ppi or lower [1].
For each PivotTable, clear Save source data with file [1].
Delete worksheets that hold unused data, then save and look at the size again.
If it is still large, try Excel Binary Workbook [1] and keep the .xlsx as well.

Where the built-in way stops

You are guessing the cause. Excel does not show what the size is made of.
Several different causes. Pictures, pivot cache, formats nothing uses and names that point nowhere each need their own step.
One file at a time. A folder of heavy workbooks means repeating this per file.
No proof the copy matches. You compare by eye.

One option: our own app

I make a Windows app for this, Reduce xlsx File Size by Hullspark. What it does, as the current code and the product page describe it:

See what makes it big. Drop .xlsx files or a folder on the window. Each file shows a bar of what its size is made of, such as sheet data, pictures and format table, and what the app found: empty cells that carry a format nobody can see, formats no cell uses, broken names, and pictures with their size.
Choose what to clean. Empty cells and rows whose only content is an invisible format, formats nothing uses, names whose whole target is gone (#REF!), the calc chain, and printer settings (off by default). Pictures: keep, standard (longest side 1,600 px, JPEG quality 82) or strong (1,024 px, quality 70). Cells with a value or formula are never removed.
A checked copy. A new file named name_small.xlsx is written next to the original. The app checks that the copy reads as a package, has the same number of sheets, and that every cell with a value or formula is in the same place with the same value. If it does not pass, nothing is kept.
Your original is never changed or overwritten. Files stay on your PC and the app makes no network connection of its own.

The free edition handles up to 3 files per run, with every option. The full edition removes the limit. It works with .xlsx. Password-protected files, .xls, .xlsb and macro workbooks (.xlsm) are named and skipped. A formula that used a removed name shows #NAME? instead of #REF! after Excel recalculates. Pictures with a rotation flag and CMYK JPEGs are left alone. The check compares file contents; it is not a look in Excel. Windows only.

Get Reduce xlsx File Size on the Microsoft Store Product page

Questions

Why is my Excel file so large when it has little data?

Common causes are formatting on millions of empty cells, formats no cell uses any more, pasted photos, a saved pivot cache and names that point nowhere. Microsoft describes formatting on unused cells as a way a workbook can grow quickly [2].

Does saving as .xlsb make the file smaller?

Microsoft lists binary format as one way to reduce size [1]. It is a different format from .xlsx, so check that everyone who needs the file can open it.

Does the app change my original file?

No. It writes name_small.xlsx next to it, or in a folder you pick.

What if the smaller copy is wrong?

After writing, the app checks that the copy reads as a package, has the same number of sheets and that every cell with a value or formula is in the same place with the same value. If it fails, nothing is kept.

Does it make a picture look smaller on the sheet?

No. The size a picture is shown at on the sheet does not change. Only the stored image is reduced.

What I have not verified

I checked the Excel claims on this page against Microsoft's two support articles on 2026-10-29. I did not re-test each menu path on every version.

I did not measure how much each built-in step saves, because it depends on the file. The Inquire statement comes from a search result summary of Microsoft's article, not a full read. The app description comes from its current code and product page. I have not tested other vendors' tools and name none.

Sources

[1] Microsoft Support: Reduce the file size of your Excel spreadsheets (fetched 2026-10-29): https://support.microsoft.com/en-us/excel/reduce-the-file-size-of-your-excel-spreadsheets
[2] Microsoft Support: Clean excess cell formatting on a worksheet in Excel for Windows (read as a search summary only): https://support.microsoft.com/en-us/excel/clean-excess-cell-formatting-on-a-worksheet-in-excel-for-windows
[3] Microsoft Store listing of the app: https://apps.microsoft.com/detail/9N48VRXRL9KN

Checked 2026-10-29. Menu names follow Microsoft's support articles for Microsoft 365 and were not checked on every version. Microsoft, Windows and Excel are trademarks of Microsoft Corporation. This page and the app are not affiliated with, made by or endorsed by Microsoft.

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