Compress Excel spreadsheets in your browser
An oversized workbook is often a small grid carrying a folder full of pictures. We re-encode those pictures and rebuild the XLSX package. Cells, formulas, charts and sheet layout stay as they are.
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No XLSX to hand?
How to compress an Excel spreadsheet
The workbook is opened in this tab and never sent away. There is no upload step or server copy.
75% quality at 1600px is generous for a sheet viewed on screen and usually removes most of the weight from pasted photos.
The result says how many pictures changed and names anything it left alone, so a cell-only workbook comes with an explanation.
The result is a normal .xlsx for Excel, Numbers, LibreOffice Calc and Google Sheets, with the same sheets and formulas.
Why pictures make an .xlsx heavy
An .xlsx is a ZIP container, not one solid binary file. Worksheets, formulas, styles and charts live in compact XML parts, while pasted photos and screenshots sit separately in xl/media. Rename a copy to .zip and that structure is visible.
Numbers and formulas compress extremely well. A workbook with a hundred thousand ordinary cells can still be smaller than one phone photograph pasted above them. Product catalogues, property schedules, inspection sheets and survey exports become large because Excel stores the original image even when it is displayed as a little thumbnail.
This tool re-encodes JPEG and PNG pictures in xl/media without changing their format or entry name, then rebuilds the surrounding package. Cell values, formulas, named ranges, filters, charts, macros, comments, print areas and workbook layout are not interpreted or rewritten.
A workbook made entirely of cells has little honest room to shrink. Its XML is already deflated inside the ZIP, so rebuilding may save only a few per cent. The result reports the number and original weight of pictures it found instead of implying that every spreadsheet should collapse.
Excel spreadsheet compression FAQ
Why is my XLSX file so large?
Usually because of pasted pictures. Excel keeps the full source photograph or screenshot even when it is displayed in a small cell-sized box. A product list with fifty thumbnails may therefore contain fifty full camera images. Ordinary cell values, formulas and styles are XML and already compress very well inside the workbook.
Will this change formulas, cells or sheet layout?
No. It only decodes JPEG and PNG parts from xl/media, writes them back under the same names and rebuilds the ZIP container. Formula XML, values, charts, filters, formatting, print areas, comments and relationships are carried through. The pictures can lose invisible detail at your chosen quality, but their anchors and displayed size do not move.
How do I make a spreadsheet small enough to email?
Turn on the target size and leave it at 10000KB. The tool tries progressively smaller versions of the embedded pictures and stops as soon as the package fits. If cells, embedded objects or fonts alone exceed the target, it says the figure is unreachable rather than deleting workbook content.
What happens to EMF and WMF pictures?
They are left alone. EMF and WMF are vector drawings rather than grids of pixels, and browser image encoders cannot safely rewrite them while preserving Office behaviour. The same is true of native Excel charts: their chart XML remains untouched. The result names recognised drawings it could not shrink.
What does “squeeze screenshots harder” do?
It reduces each embedded PNG to a palette of at most 256 colours before encoding it again. Screenshots, diagrams and flat-colour exports often become dramatically smaller with no obvious visual change. A photograph stored as PNG may show banding in smooth skies or gradients, which is why the switch is off by default.
Can it compress an old .xls file or a password-protected workbook?
No. The old .xls format is a binary workbook rather than this ZIP-based format; open it in Excel or LibreOffice and save it as .xlsx first. Encrypted or password-protected XLSX packages cannot be read without decrypting them, so they are refused rather than returned damaged.
Why did a workbook with thousands of rows barely shrink?
Rows of text and numbers are already tiny after ZIP deflate, and repeated values compress especially well. If the workbook has no JPEG or PNG pictures, rebuilding the package is the only available saving and that is usually a few per cent. Removing formulas or data to manufacture a larger number would not be compression.
Is my spreadsheet uploaded anywhere?
No. Reading, picture re-encoding and ZIP writing happen in JavaScript in this browser tab. Once the page has loaded, your workbook does not become a network request and no server receives a copy.
Related
Same format joins the queue. Anything else re-routes to its own tool.