How to convert XLS to XLSX
- Choose your .xls files. Pick one or drop a whole folder’s worth at once. Each file is checked first, so damaged or password-encrypted files are flagged before anything runs.
- Decide how you want them back. With several files you get a ZIP with one .xlsx per file, or a single workbook with every sheet from every file.
- Click Convert to XLSX. Every sheet, value and formula is copied, along with number formats, merged cells, column widths and comments.
- Download. The report under each file tells you how many sheets, rows and formulas were converted, and warns you about anything that could not be copied.
Private by design: nothing is uploaded
The conversion runs inside your browser, in a background worker on your own device. There is no server that receives your spreadsheets: the page only downloads its own code and the open-source SheetJS library from this site. You can check it in the Network tab of your browser’s developer tools, or go offline once the page has loaded and keep converting.
That matters for the kind of files that still live in .xls: old accounting books, payroll archives, customer lists and supplier price lists.
What is an .xls file?
.xls is the binary format used by Excel 97, 2000, 2002 (XP) and 2003, known as BIFF8. The workbook is stored as binary records inside an OLE compound file, the same container used by old .doc and .ppt files. Since Excel 2007 the default is .xlsx (Office Open XML, standardised as ECMA-376 and ISO/IEC 29500): a ZIP package of XML files that is usually smaller and easier for other programs to read.
Every current version of Excel still opens .xls, but in Compatibility Mode: the title bar says so, and the workbook keeps the old limits until you save it in the new format.
Why convert XLS to XLSX
- More rows and columns.xls stops at 65,536 rows and 256 columns (column IV). .xlsx goes up to 1,048,576 rows and 16,384 columns (XFD).
- Leave Compatibility ModeNewer functions and features are limited while a workbook is still an .xls.
- Works with modern toolsPython’s openpyxl, many web apps and import wizards accept .xlsx but not the old binary format.
- No hidden macrosAn .xls can carry VBA macros. An .xlsx cannot (macro workbooks must be .xlsm), so it is safer to share.
- Smaller files.xlsx is ZIP-compressed XML; text-heavy workbooks often shrink noticeably.
- Archive clean-upConvert years of exported reports in one go instead of opening and saving each file in Excel.
Convert many XLS files to XLSX at once
Excel can only convert one open workbook at a time (File › Save As, or File › Info › Convert on Windows); doing a whole folder means a macro or a lot of clicking. Here you drop all the files together and get them back as a ZIP, with the same names and the .xlsx extension, or merged into one workbook where each sheet keeps its name (or takes the file name when names repeat). The files are converted one after another in the background, so the page stays responsive.
What is kept and what is not
We tested the converter with .xls files saved by Microsoft Excel and then opened the results in Excel.
Kept
- All sheets, their names and order, and hidden sheets
- Values, text with accents and other alphabets, dates
- Formulas (for example
=SUM(D2:D4)) with their last calculated result
- Number formats such as
#,##0.00 "€" or yyyy-mm-dd
- Merged cells, column widths and row heights
- Cell comments, hyperlinks and defined names
Not kept
- Fonts, bold, colours, fills, borders and alignment: the result uses Excel’s default style
- Conditional formatting and data validation
- Charts, pictures and shapes (the data behind a chart is kept)
- Macros (VBA) and pivot tables (the values they show stay as cells)
- Anything else, such as freeze panes, print setup or sheet protection, should be treated as lost
If you need the formatting exactly as it was, open the file in Excel and use Save As › Excel Workbook (.xlsx). Use this converter when what matters is the data, or when you have many files.
XLSX to XLS: when you need the old format
Some old programs, upload portals and Excel 2003 users still only accept .xls. Switch the direction to XLSX → XLS and the converter writes a BIFF8 workbook, but the old format has hard limits, and the converter checks them and tells you exactly what was lost:
- 65,536 rows × 256 columns per sheet. Anything below row 65,536 or right of column IV is left out, and you are told how many cells and which sheets.
- Formulas are saved as values. The free engine used here cannot write .xls formulas, so each cell keeps its last calculated result.
- Texts longer than 255 characters are cut to 255 characters, and the number of affected cells is reported.
- Styles are not copied in this direction either.
Known limitations
- .xls files encrypted with a password to open (RC4, the method Excel has used since 2002) cannot be opened here. Open the file in Excel, remove the password and save it, then convert it.
- Very old Excel 5.0/95 files are usually readable, but they were not part of our tests.
- There is no file size limit or quota. Conversion happens in memory, so very large workbooks need a computer with enough RAM; on phones, keep files under about 20 MB.