Documents

What is an XLSX file?

Updated Jul 2026

Definition

XLSX is the standard file format for spreadsheets, storing rows, columns, formulas, and formatting in a single document. It's a lossless, structured format, so numbers and calculations stay exact rather than approximated. The main limitation is that not every app opens it cleanly, and some tools flatten formulas into static values when converting.

XLSXExcel spreadsheet

Extension: .xlsx
Type: Documents
Typically: Spreadsheets

Why XLSX exists

XLSX became the default spreadsheet format in 2007, replacing the older XLS format with a structure based on XML packed into a zipped folder. That change made files smaller and less prone to corruption, and it's why the format has stuck around largely unchanged since.

Underneath, an XLSX file is really a small archive of text files describing each sheet, its cells, styles, and any formulas or charts. That structure is what lets a spreadsheet hold live calculations instead of just a grid of numbers, so a total updates automatically when you change a number above it.

People run into XLSX conversion when they need a plain, universal version of the data. A CSV export strips out formatting and formulas so the numbers can be imported somewhere else, and a PDF export locks the layout so a report looks the same on any screen.

The friction shows up when a formula-heavy workbook needs to become one flat table, or when someone without spreadsheet software just needs to read the numbers.

The trade-offs

Strengths

Keeps formulas, formatting, and multiple sheets in one file
Widely supported across desktop, web, and mobile apps
Lossless: numbers and calculations stay exact, not rounded

Watch-outs

Formulas can break or shift when moved between apps
Not ideal for simple data sharing; CSV is lighter and more universal
Can carry hidden sheets, cached values, or old edit history

A note on privacy

An XLSX file can carry more than the visible cells: author names, edit history, hidden sheets, and cached formula results can all sit inside the file even after you think you've cleaned it up. Uploading that file to an online converter means all of that goes to a server you don't control. Converting on your own machine keeps the spreadsheet, and anything hidden inside it, off the internet entirely.

Convert an XLSX file

Questions

How do I open an XLSX file?

Most spreadsheet apps on Mac, Windows, and mobile open XLSX directly, and many free viewers and web apps support it too. If nothing on your device opens it, converting to CSV or PDF lets you see the data without needing a spreadsheet app at all.

Is XLSX better than CSV?

XLSX keeps formulas, formatting, and multiple sheets, which CSV can't do. CSV wins when you just need plain rows of data that any system can read without extra software.

Why does my file save as XLSX instead of XLS?

XLS is the older format from before 2007. Modern spreadsheet software defaults to XLSX because it's smaller, more reliable, and less likely to corrupt.

Can I convert XLSX without uploading it?

Yes. A desktop app like Morphjet converts XLSX to CSV, PDF, or other formats on your own computer, so the spreadsheet and anything hidden inside it never leave your machine.

Morphjet opens and converts XLSX and 1,800+ other formats, all on your own computer. Launching this July.