How to use the Spreadsheet Converter converter
- Add filesClick “Choose Files” or drag them in. Each file is detected automatically, and you can mix different formats in one batch.
- Pick the output formatUse the “to” menu next to each file to choose the target format (XLSX is preselected).
- Convert and saveHit “Convert”. Everything is processed on your device, then you can download each result or a ZIP of all of them.
About XLSX
XLSX Microsoft Excel Workbook
XLSX is the standard Excel spreadsheet format with multiple sheets, formulas and formatting. Google Sheets, Numbers and LibreOffice open it too.
- Compression
- ZIP-compressed XML
- Features
- Multiple sheets, formulas
- Origin
- 2007, Microsoft
- Best for
- Spreadsheets, reports
Why use ConvertMathly?
Files are processed on your device and never uploaded. Close the tab and they are gone.
No account, no daily cap, no queue and no watermark — convert as much as you want.
No waiting for uploads or downloads: results are ready as fast as your device can process them.
Windows, Mac, Linux, Chromebook, iPhone and Android — any modern browser, nothing to install.
Frequently asked questions
What formats does the Spreadsheet Converter support?
It accepts XLSX, XLS, CSV, ODS, TSV, JSON and more, and can output XLSX, CSV, JSON, HTML, ODS, TSV.
Is it really free?
Yes. ConvertMathly is free with no sign-up, no watermarks and no limits. The site is supported by ads.
Are my files private?
Completely. Conversion happens inside your browser — files are never uploaded to any server.
Does it work on iPhone and Android?
Yes, the converter works in Safari, Chrome, Firefox and Edge on phones, tablets and computers.