You send the quote in XLSX and the client replies: "our ERP only accepts Excel 2003 XLS." Or the warehouse machine has Office 2007 without patches and will not open modern files. Going from xlsx to xls is the bridge between your current Excel and their fossilized infrastructure.
XLSX is compressed XML with more rows and functions; XLS is legacy binary with lower limits. Converting does not add infinite compatibility — 65536 rows in old XLS — but it unlocks many corporate imports. FORMARTIO converts in the browser without extra Office licenses.
When you need xlsx to xls
Imports to old SAP, inherited macros, logistics vendors, agencies with old templates, industrial equipment that only exports XLS. Also when someone confuses formats and rejects the attachment without reading the real error.
If the limit is rows or columns, format conversion is not magic: you may need to split the file into two sheets.
Step by step to convert XLSX to XLS
- Open XLSX to XLS on FORMARTIO.
- Upload the XLSX workbook. Check it has no modern macros XLS will not support.
- Start conversion and wait for processing.
- Download the XLS and open it in the client's old Excel or LibreOffice in compat mode.
- Verify critical formulas and date formats before sending final version.
What can be lost in conversion
Modern structured tables, some 3D charts, slicers, recent functions XLS does not understand. Cells may become static values if the formula does not exist in legacy.
Complex conditional formatting sometimes simplifies. For rich visual reports, PDF is better; for tabular data, xlsx to xls is usually enough.
Dates and decimals
Excel in Spanish vs English interprets dates differently by locale. After converting, check the date column: 36526 or 01/01/2000? Adjust cell format before ERP import.
Comma vs dot decimal separator in intermediate CSV does not apply the same in binary XLS, but formulas with DECIMAL may vary. Test import in client staging environment.
Alternatives if XLS also fails
Exporting UTF-8 CSV from source is sometimes more universal than XLS. You lose formulas but gain simplicity in databases.
Ask the client to update the template: sometimes "XLS only" is a myth kept alive by a 1998 script nobody dares touch.
Best practices when sending
Name the file clearly — Quote-2026-05.xls. Attach a note with tested Excel version. Keep XLSX master on your side; XLS is delivery, not working file.
If the ERP requires columns in fixed order, validate headers after xlsx to xls before bulk load that rolls back half the inventory.
Password on XLSX does not always survive the same; confirm receiver security policy.
Multiple sheets in XLSX: confirm all migrated to XLS; sometimes only the active sheet converts and the client loses auxiliary tabs without clear warning.
xlsx to xls in the supply chain
Vendor asks for XLS template with fixed columns: do not add extra columns after converting; rigid importers fail silently or drop entire rows.
Version the file — inventory-v3.xls — in the name when resending; xlsx to xls over old data without notice creates double entry in the confused client warehouse.
When your XLSX gets rejected for compatibility and you do not have a PC with Office 2003 handy, convert XLSX to XLS on FORMARTIO, test key formulas, and send the format the other system actually accepts.