XLS files are binary Excel workbooks compatible with older versions of Microsoft Office.
Common Uses
Working with legacy Excel files
Compatibility with older systems
Spreadsheet data storage
XLS Conversion FAQ
What is an XLS file?
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XLS is the binary file codec used by Microsoft Excel 97-2003.
Do formulas survive when I convert an XLS?
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Only into another real spreadsheet format. Convert XLS to a spreadsheet and formulas, references and named ranges round-trip intact. Convert to a flat data or page format and every cell is frozen at its last computed value — the number stays, the calculation behind it does not. That is usually what you want for sharing and never what you want for continued work. An XLS is an OLE compound file holding sheets, formulas, formatting and any VBA macros as binary streams.
Why is XLS the format everyone at work sends?
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Because it is what the software on the machine saves by default, and defaults decide almost everything about which formats spread. The awkward cases are the predictable ones: a recipient on different software, an older version, or a system that only accepts one specific format for upload. All three are one conversion away from working. XLS is the binary Microsoft Excel workbook format from Excel 97 through Excel 2003.
Why does newer software warn me when I open an XLS?
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Because it is the pre-2007 binary format, and binary Office documents are a well-known malware delivery route — the warning is about the container, not about your file. The modern replacement is a zipped XML package that is safer to parse, smaller on disk and readable by tools that are not Microsoft's. Converting is the way out of the warning, and the content survives it intact. XLS caps out at 65,536 rows and 256 columns, and its macro payloads make it a recurring security problem.
What happens to multiple sheets when I convert an XLS?
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It depends whether the target knows what a sheet is. Another workbook format keeps them all, in order, with their names. A flat data format keeps exactly one, normally the first, and drops the rest without comment — the single most common way to lose data in a spreadsheet conversion. A page format renders each sheet in turn, so nothing is lost, but nothing stays calculable either.
Why is an XLS so awkward to read on a phone?
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Because a grid cannot reflow. Text rewraps to a narrow screen; a row of eighteen columns cannot, so the choice is scrolling sideways or shrinking everything until the numbers are unreadable. Converting to a fixed page keeps the grid and makes zooming predictable; converting to a document turns each sheet into a table that reads properly in one column, at the cost of being able to recalculate anything.
Should I still be saving new files as XLS?
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Only if something downstream demands it. The format still opens, and there is no urgency about converting an archive that is not causing trouble, but it is no longer where the tooling or the efficiency is going. For anything new, a current format costs nothing extra and avoids the next round of this question a few years from now.
Are cell references between sheets kept when converting XLS?
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Between real spreadsheet formats, yes — cross-sheet references, named ranges and defined formats travel with the file. Anything flatter than a spreadsheet has no concept of a reference, so it stores the value the reference resolved to at the moment of conversion. A workbook that pulls from other files should be checked after conversion rather than assumed correct.
Does it matter that XLS is over thirty years old?
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Age itself is not the problem — several formats from that era are still perfectly good, precisely because everything has had decades to implement them. What matters is what the era assumed: small files, modest processors, no network, and features nobody needed yet. Where those assumptions still fit, the format is fine. Where they do not, that is the reason to convert.
Can I keep editing after converting my XLS?
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That depends entirely on the target. Converting to another editable document format keeps the structure — styles, headings, tables — so work continues normally. Converting to a page or image format produces something for reading rather than writing, and getting back from there means a second conversion that reconstructs structure rather than restoring it. Keep the XLS as the working copy either way.
Do I need the Microsoft software that made this XLS?
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Not to convert it. The format is Microsoft's and its own applications handle it best, but the file is readable by other tools and the conversion here runs server-side — nothing is installed and no licence is needed. Fidelity is the honest caveat: features specific to the original application are approximated rather than reproduced exactly.
Can I convert a whole folder of XLS files in one go?
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With an account, yes — drop them in together and they are queued as one job rather than handled one at a time, with the same settings applied across the batch and the results returned together. Free conversions run a single file at a time (merge tools take two); a paid plan is what unlocks batch processing and the larger per-file limit, which is what makes converting a whole archive practical.
