Free online WK1 to XLSX converter

Older accounting, inventory, and business records may still exist as .wk1 files, while current spreadsheet software usually expects .xlsx. Converting the file makes its data editable in supported spreadsheet applications and easier to share or archive.

What the WK1 format is

WK1 is the binary worksheet format used by early versions of Lotus 1-2-3, especially the DOS-era releases before the later WK3 and WK4 formats. It can contain cell values, formulas, basic number formats, text alignment, column widths, ranges, and other Lotus 1-2-3 worksheet metadata.

WK1 files are usually encountered in archives from older businesses, government offices, accounting systems, and personal computers. They are spreadsheet files, not word-processing documents. Modern Microsoft Excel versions generally do not provide dependable WK1 import, so opening the file directly in Excel is not a reliable conversion method.

What the XLSX format is

XLSX is the XML-based Microsoft Excel workbook format defined by Office Open XML. It is supported by current Excel, LibreOffice Calc, Apple Numbers, Google Sheets after import, and many document-management systems.

An XLSX workbook can contain multiple worksheets, formulas, formatting, tables, filters, charts, and larger grids than the original WK1 format. Its files are ZIP packages containing XML and related resources; compression often reduces size, although the result is not guaranteed to be smaller than every older spreadsheet file.

How to convert WK1 to XLSX

Using LibreOffice Calc

1. Make a backup of the original filename.wk1 before opening or converting it.
2. Install a current desktop version of LibreOffice and open Calc.
3. Select File → Open, choose the WK1 file, and let Calc use its Lotus 1-2-3 import filter.
4. Check the imported values, formulas, worksheet structure, dates, number formats, column widths, hidden rows and columns, and totals.
5. Select File → Save As, choose Excel 2007–365 (*.xlsx), and save the result as filename.xlsx.
6. If Calc warns that some features may not be preserved, choose the option to use the XLSX format, then reopen the saved file and check it again.

For repeated conversions, LibreOffice can be run without its graphical interface:

libreoffice --headless --convert-to xlsx --outdir converted filename.wk1

The command depends on LibreOffice having a working WK1 import filter. Test one file first, and inspect the output manually because headless conversion does not show every import warning or layout change.

Using 101convert

You can convert a .wk1 file on 101convert.com for free without installing software. Upload the file, select XLSX as the output format, start the conversion, and download the resulting .xlsx file. Do not upload confidential financial, personal, or business records unless the service's privacy and retention terms meet your requirements.

Quality and compatibility limitations

The conversion transfers existing worksheet content into a newer container; it does not add modern Excel features to the original data. Lotus 1-2-3 formulas, obsolete functions, external references, named ranges, and date conventions may be translated, recalculated differently, or removed.

Charts, print settings, page breaks, hidden content, macro sheets, linked files, and Lotus-specific metadata may not survive. Compare important totals and formulas with the original, inspect dates and decimal separators, and verify that every worksheet and range was imported. If the file cannot be opened by LibreOffice or 101convert, a copy of the appropriate historical Lotus 1-2-3 software or a legacy conversion environment may be required.