XLSX to XLS for older Excel versions and legacy imports

Going backwards is sometimes required. A tax portal, an old accounting package or a customer on Excel 2003 needs .xls, and saving down in Excel shows a compatibility checker full of warnings that nobody reads.

XlsConverter writes a real XLS file and tells you exactly what had to change to fit the older format. For the opposite upgrade see XLS to XLSX, and if the target system accepts plain text, XLSX to CSV avoids the old limits altogether.

How to convert XLSX to XLS in three steps

1. 1Upload the XLSX workbook.
2. 2Choose how rows and columns over the XLS limits are handled.
3. 3Convert, download the XLS file and review the compatibility report.

Functions and limits that do not exist in the XLS format

Functions added after 2003 have no place in XLS. IFERROR, SUMIFS, COUNTIFS and AVERAGEIFS came in 2007, and XLOOKUP, FILTER, UNIQUE and dynamic arrays came much later. A formula using them would show #NAME in old Excel. We replace such formulas with their calculated values and list each affected cell, so the numbers stay right even where the formula cannot.

The size limits are hard: 65,536 rows, 256 columns, and 4,000 unique cell formats per workbook. A modern sheet with 200,000 rows becomes four sheets, and a workbook with many style variations has similar formats merged. Conditional formatting is limited to three conditions per range in XLS, so rules beyond that are dropped and reported.

Colors are restricted to a palette of 56 entries, so brand colors are mapped to the nearest available color. Text is stored as Unicode, so non Latin characters survive. If the receiving program actually wants delimited text despite asking for Excel, CSV to XLS or a tab separated export can be cleaner.