How XLS to XLSX Conversion Works
The converter reads the binary workbook, including every sheet, formula, number format and chart it can resolve, and writes it out as an XLSX package.
Formulas stay formulas rather than being replaced with their results, so the workbook keeps recalculating after the upgrade.
Why Upgrade From XLS
The old format stops at 65,536 rows and 256 columns. XLSX goes to 1,048,576 rows and 16,384 columns, which is the difference between truncating an export and keeping it.
XLSX also compresses far better, supports more conditional formatting and is readable by data tools, so a workbook stops being a dead end for automation.
Common Use Cases
Reviving a workbook from an old server or a legacy accounting system so current Excel, Google Sheets or Numbers can work with it properly.
Feeding a spreadsheet into a data pipeline, a Python script or an import form that expects XLSX and cannot read the binary format.
What Carries Over
Sheets, cell values, formulas, named ranges, number and date formats, cell styles, conditional formatting, charts and print settings carry over.
Macros do not: a workbook with VBA needs the .xlsm format, so keep the original if your sheet runs code. Very old chart types can also be redrawn with a modern equivalent.
Tips Before You Convert
Open the result and check the totals on a sheet you know. A matching grand total is the fastest proof that formulas and number formats came through intact.
If the workbook pulls data from another file, reconnect that link after conversion, because the path is stored inside the workbook and may still point at the old location.