Excel XLS to Excel XLSX converter

XLS to XLSX resolves to our table engine in this app, so the legacy workbook is parsed into tables and rebuilt as a value-only XLSX.

Converted with Table engine · nothing stored
Free: 5 conversions a day · 5 MB each
Higher limits →

From real runs

What you get — and what changes

Element	Result	What happens
Worksheets	Kept	The Pipeline and Notes sheets were both present in workbook.xml after conversion from the rich XLS fixture.
Cell text	Kept	Company names, owner initials, stage labels, and second-sheet notes remained visible in the generated XLSX XML.
Numbers	Kept	ARR cells such as 48000 and 120000 were written as numeric XLSX cells without a string type marker.
Dates	Changed	Date cells were serialized as ISO timestamp strings such as 2026-10-14T00:00:00.000Z rather than Excel date serials.
Formulas	Lost	The SUM(C3:C6) total became the cached value 254500; no formula attribute was present in sheet1.xml.
Merged header	Changed	The merged Q3 Pipeline header expanded into Q3 Pipeline plus generated column_2 through column_5 labels.
Formatting and charts	Lost	Column widths, styles, comments, pinned panes, charts, and merge metadata are not retained by the tabular IR rebuild.

Worksheets Kept
The Pipeline and Notes sheets were both present in workbook.xml after conversion from the rich XLS fixture.
Cell text Kept
Company names, owner initials, stage labels, and second-sheet notes remained visible in the generated XLSX XML.
Numbers Kept
ARR cells such as 48000 and 120000 were written as numeric XLSX cells without a string type marker.
Dates Changed
Date cells were serialized as ISO timestamp strings such as 2026-10-14T00:00:00.000Z rather than Excel date serials.
Formulas Lost
The SUM(C3:C6) total became the cached value 254500; no formula attribute was present in sheet1.xml.
Merged header Changed
The merged Q3 Pipeline header expanded into Q3 Pipeline plus generated column_2 through column_5 labels.
Formatting and charts Lost
Column widths, styles, comments, pinned panes, charts, and merge metadata are not retained by the tabular IR rebuild.

Sample conversions

Two-sheet pipeline workbook

Input: Legacy XLS with Pipeline and Notes sheets, a merged Q3 Pipeline heading, ISO-like dates, ARR numbers, and a cached SUM total.
Output: XLSX kept both sheets and numeric ARR values. The formula was only 254500, and dates were timestamp strings in the worksheet XML.

Simple fixture workbook

Input: Sample XLS with Pipeline rows for Northwind, Contoso, Fabrikam, and Tailspin plus a Notes sheet.
Output: The XLSX had sheet1 and sheet2 with the same row text. Numeric arr cells were numbers, while close_date cells stayed strings.

A real Excel XLS → Excel XLSX run

We converted our Excel XLS sample (5 KB) with Table engine on 2026-10-20. It took 4 ms and produced a 18 KB Excel XLSX file, 4.0× larger than the input. The engine raised 1 warning, listed below.

Input · sample.xls · 5 KB

OLE2 compound document (legacy Office binary)

Output · sample.xlsx · 18 KB

Workbook with 2 sheets (Pipeline, Notes); first sheet 5 rows, 25 cells, 0 formulas, header filter, fitted column widths

Sheets: 2
Sheet names: Pipeline, Notes
Rows: 5
Cells: 25
Formulas: 0
Header filter: yes
Column widths: fitted

Workbook contains multiple sheets; each sheet was exposed as its own IR table.

Options and when to change them

sheet: Choose a worksheet when you want only one source sheet rebuilt instead of every sheet in the XLS.
headerRowIndex: Set this when a workbook has a title row above the real field names, as our Q3 Pipeline fixture did.
dateHandling: Use string handling when the displayed date text matters more than typed spreadsheet date values.

Do it yourself

LibreOffice

bash

soffice --headless --convert-to xlsx workbook.xls --outdir .

LibreOffice is a better fidelity-preserving path than tabular-ir if formulas, merges, and styles must survive.

Excel XLS to Excel XLSX by API or MCP

The HTTP API and the MCP server run the exact engine this page uses (Table engine); the response carries the same warnings the web converter shows. Check support first with GET /api/v1/pairs?from=xls&to=xlsx.

curl

curl -X POST https://filetypeconverters.com/api/v1/convert \
  -H "Authorization: Bearer $FTC_API_KEY" \
  -F "file=@input.xls" -F "from=xls" -F "to=xlsx" \
  -F 'options={"sheet":""}' \
  --output output.xlsx

Options this engine accepts for Excel XLS → Excel XLSX

Key	Applies to	Type	Default
sheet	Reading Excel XLS	string
headerRowIndex	Reading Excel XLS	number	0
dateHandling	Reading Excel XLS	date · string	date
sheetName	Writing Excel XLSX	string

API reference

When this is the wrong conversion

Do not use this route when formulas, charts, merged cells, or workbook styling are the reason you need XLSX.
Use /convert/xls-to-pdf when the goal is a visual snapshot of the workbook rather than editable table data.

Excel XLS to Excel XLSX questions

Why are formulas missing after XLS to XLSX?

This pair uses our table engine, which reads cached values and writes a new workbook from table data. Formula expressions are not part of the output model.

Does XLS to XLSX keep multiple sheets?

Yes when no sheet is selected. Our Pipeline and Notes tabs both appeared in the resulting workbook package.

Why did a merged title become extra columns?

The parser turns a rectangular sheet into a table. Empty cells under a merged title need generated names such as column_2 so the output has a complete header row.