Add your XLS file
Drop one or more .xls files onto the converter above, or browse for them. They load into browser memory only — nothing is uploaded, so there is no size-based pricing and no server queue.
XLS to XLSX
Converting a .xls file to .xlsx extracts the document's content from its office package into a portable form. Free, private, and validated — the file never leaves your browser.
Private for supported formats — processed in your browser
Runs on your deviceConvert supported files
Drop XLS files here
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.About converting Excel workbook to Excel workbook
Converting a .xls file to .xlsx extracts the document's content from its office package into a portable form. An .xls file is a legacy Microsoft Excel workbook in the binary BIFF format, Excel's default from its earliest releases through Excel 2003. Each sheet is a stream of typed binary records — cells, formulas, formats — rather than anything textual.
An .xlsx file is a modern Excel workbook — a ZIP archive of SpreadsheetML XML parts describing sheets, shared strings, styles, and formulas. It has been Excel's default save format since 2007 and the de facto interchange format for tabular business data. For this route the practical draw is vast grid limits compared with the legacy .xls format and documented ZIP-of-XML anatomy — any ZIP and XML library can mine it, which is how in-browser conversion works here — balanced against date-as-serial-number storage causes subtle off-by-one and timezone bugs, which is worth knowing before you commit a large batch.
Why convert XLS to XLSX?
The practical trigger for this conversion is usually a mismatch: with .xls, the 65,536-row ceiling truncates modern datasets. Switching to .xlsx buys you vast grid limits compared with the legacy .xls format, which is why it is the better fit for the standard vehicle for exchanging spreadsheets between organizations. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
XLS vs XLSX at a glance
| Aspect | Excel workbook (.xls) | Excel workbook (.xlsx) |
|---|---|---|
| Format type | Text-based — characters and structure, so there is no visual quality loss | Text-based — characters and structure, so there is no visual quality loss |
| How it stores data | composed of typed binary records (id, length, payload) — LABELSST for shared-string cells, FORMULA for calculations, and hundreds more | xl/worksheets/sheetN.xml holds rows of typed cells; text cells usually point into xl/sharedStrings.xml to avoid repetition |
| Strongest at | reading exports from ERP, banking, and lab systems that still emit .xls | the standard vehicle for exchanging spreadsheets between organizations |
| Weak spot | the 65,536-row ceiling truncates modern datasets | date-as-serial-number storage causes subtle off-by-one and timezone bugs |
| Metadata | summaryInformation streams in the compound file record author, company, and creation and modification timestamps | docProps/core.xml carries Dublin Core creator and date fields while docProps/app.xml records the generating application and company — both ride inside the ZIP |
Pick XLSX as the output
Select .xlsx in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if XLSX is selectable, the route is real and validated.
Convert on your device
Press Convert. The package is unzipped in memory and its XML content parsed locally; nothing is uploaded.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid XLSX file. Outputs keep the original filename with the .xlsx extension.
XLS to XLSX questions, answered
Will converting XLS to XLSX lose quality?
There is no visual quality to lose — xls is text-oriented and xlsx is text-oriented, so the question is structural fidelity. Text, ordering, and basic structure are preserved; complex layout, embedded objects, and styling beyond the target's model are simplified.
Is it private to convert XLS files here?
Yes — the .xls file is processed inside your browser tab and never uploaded. The package is unzipped in memory and its XML content parsed locally; nothing is uploaded. Close the tab and the file is gone from memory.
Where will the XLSX file work?
Excel 2007 onward, LibreOffice Calc, Google Sheets, and Apple Numbers all handle .xlsx, and nearly every data-processing library reads it. Support is equally solid on iOS and Android through the same vendors' apps.
Will the XLSX file be bigger or smaller than my XLS?
It depends on the content: xl/worksheets/sheetN.xml holds rows of typed cells; text cells usually point into xl/sharedStrings.xml to avoid repetition. Convert one representative file first and compare before batch-processing a large set.
What happens to the metadata in my XLS file?
In .xls, summaryInformation streams in the compound file record author, company, and creation and modification timestamps. Re-encoding through the browser pipeline does not carry embedded metadata into the output, which doubles as a privacy scrub — check the exported file if you specifically need tags preserved.