How to Convert XLS to XLSX

An .xls file turns up — from an old archive, an accountant, a government download, a machine that has been printing reports the same way since 2004 — and something refuses to cooperate. Excel blocks it, a web app rejects the upload, or an import script only knows how to read .xlsx.

Converting it to .xlsx fixes all three, and it takes about ten seconds.

What actually changed between XLS and XLSX

.xls is the binary format Excel used up to 2003. Everything — cells, formulas, formatting, charts, macros — is packed into one opaque binary blob that only Excel truly understood.

.xlsx, introduced with Excel 2007, is a zip archive full of XML. Open, documented, readable by every spreadsheet application and by ordinary programming libraries. Practical consequences of the change:

• Room to grow. XLS caps out at 65,536 rows and 256 columns. XLSX allows 1,048,576 rows and 16,384 columns. If your old file has been quietly truncating data at row 65,536, this conversion is the fix.
• Smaller files. XML compresses well; converted files are often dramatically smaller than the binary original.
• Fewer refusals. Anything that imports spreadsheets today expects XLSX. Support for the old binary format is patchy and shrinking.
• Safer. XLSX cannot contain VBA macros at all — which is exactly why modern Office blocks old files by default (more on that next).

Why Excel may be refusing to open your XLS at all

If Excel greets your file with a message about the file type being blocked by your security settings, or blocked because it came from the internet, you are not doing anything wrong. Microsoft tightened the default policy on legacy binary formats because they were a favourite carrier for macro-based malware.

You can dig through Trust Center settings to unblock it. Converting the file is usually quicker, and it leaves you with something that will not trip the same policy again next month.

Convert XLS to XLSX, step by step

1. Open the converter. Go to the XLS to XLSX tool and drop in your .xls file.
2. Convert. LibreOffice reads the binary format on our server and writes a proper XLSX — sheets, formulas, number formats and cell styling carried across.
3. Download the .xlsx and open it anywhere: Excel, Google Sheets, Numbers, LibreOffice, or your import script.

No Excel licence required at any point, which is the entire reason to do it this way.

The macro trap

This is the one thing worth reading twice. XLSX cannot store macros. It is a deliberate property of the format, not a limitation of any converter.

So if your old workbook contains VBA — buttons that do things, an auto-run routine, a custom function used in cells — that code does not survive the conversion. Formulas and data are fine; the programming is not. Custom VBA functions will come through as #NAME? errors, because the function they referred to no longer exists.

If the macros matter, you need .xlsm (macro-enabled workbook) instead, and that means opening the file in Excel or LibreOffice and saving it yourself. If you only need the numbers — which is the usual case for an archived file — XLSX is exactly right, and losing decades-old VBA is a feature.

What else to check after converting

Data and formulas transfer reliably. These are the areas where an old file can shift slightly, so give them a glance:

• Charts. Chart types and data ranges come across; fine styling on very old charts can be reinterpreted.
• Conditional formatting. Modern rules are richer than what XLS could express, and complex old rules occasionally simplify.
• Pivot tables. Usually survive, but refresh them once and confirm the source range is still what you expect.
• Links to other workbooks. External references still point at .xls filenames. If you are converting a whole set of linked files, the links will need repointing.
• Dates before 1900. Spreadsheet date systems have famous edge cases around 1900. If a file contains genuinely ancient dates, spot-check them.
• Fonts. A font the file expects that is not installed gets substituted, so column widths can look slightly different. Content is unaffected.

Where to go from XLSX

• Feeding it to a database, a script or an import routine? Excel to CSV gives you plain rows.
• Sending it to someone who should read but not edit it? Excel to PDF.
• Have old Word documents from the same era? DOC to DOCX is the same job for text.

Is it private and free?

Reading the legacy binary format properly needs a real office engine, so this converter runs on our secure server rather than in your browser. Your file is uploaded over an encrypted HTTPS connection, converted in an isolated workspace, and deleted automatically the moment the XLSX is sent back— nothing is stored, logged or shared. Free: no watermark, no sign-up, no daily limit, files up to 100 MB.

That said, use your judgement. For a workbook of genuinely sensitive financial or personal data, converting locally in Excel or LibreOffice keeps the file on your own machine, and that is the more cautious choice.

Frequently asked questions

Will my formulas still work? Yes. Standard formulas convert directly — the formula language did not change. Only custom VBA functions break.

Do I lose data? No. Cell values, sheets, number formats and most styling come across. Macros are the deliberate exception.

Can I do this in Excel instead?Yes — File › Save As › Excel Workbook. If you have Excel and it will open the file, that is the most faithful route. This tool exists for when you do not, or when Excel is blocking the file.

Does it handle multiple sheets? Yes, all sheets and their tab order and names.

What about .xlsb files? Not accepted here — that is a different binary format again. Only .xls goes in.

Can I convert XLSX back to XLS? Not with this tool, and it is rarely wise: you would reintroduce the row limit and the security blocks. If a system truly requires the old format, CSV is usually accepted too and is far less trouble.

Convert your spreadsheet now

Open the XLS to XLSX converter, drop in the old file, and get a modern workbook back in seconds — free, watermark-free and deleted right after.