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Drop one XLS or two hundred. Batch conversion is not a paid feature here.
Convert XLS to XLSX
An old workbook from an archive or a legacy system has to work in current Excel or Google Sheets without compatibility warnings.
SafeConvert engineFreeNo sign-upBatch supported
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What actually changes
XLS and XLSX are not the same picture in two wrappers.
The binary BIFF file is rewritten as a ZIP of XML parts. The 65,536 row and 256 column limits of the old format are lifted to 1,048,576 rows and 16,384 columns, and the file usually shrinks considerably.
Worth knowing first
Macros do not survive. XLSX is defined as macro-free, so any VBA in the original is dropped, and preserving it means converting to XLSM instead. Old workbooks with automation are exactly the ones most likely to have it.
Questions
XLS to XLSX, answered
Will my formulas still work?
Yes. The formula language is unchanged. Only functions added after the original file was written might display differently in old readers.
Why is the XLSX smaller?
It is a ZIP archive internally, and XML compresses very well. Halving the size is normal.
How to convert XLS to XLSX
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Choose your settings
Excel Workbook is lossless, so nothing is thrown away in the conversion.
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Download
Converted and deleted the moment it finishes. Never written to permanent storage.