CSV vs XLSX
CSV is plain data that any program can read; XLSX is a full Excel workbook. Picking the wrong one loses either formatting or compatibility.
| Feature | CSV | XLSX |
|---|---|---|
| What it is | Plain text table | ZIP of XML files |
| Sheets | One | Many |
| Formulas | No (values only) | Yes |
| Formatting and charts | No | Yes |
| Data types | All text | Numbers, dates, text, booleans |
| Readable by | Everything: Excel, databases, code | Spreadsheet apps, libraries |
| Row limit | None | 1,048,576 per sheet |
What's inside each file
A CSV file is plain text. Each line is a row and commas separate the values. There are no fonts, colours, column widths, formulas or multiple sheets, and every value is just text; it's up to the program reading the file to decide that 2024-01-05 is a date or 007 is a number.
An XLSX file is a ZIP archive containing XML files that describe each sheet's cells, their types and formulas, shared strings, styles, charts, images, and more. It can store everything you see in Excel.
Compatibility
CSV is the universal exchange format for tabular data. Databases, CRMs, accounting tools, analytics platforms and every programming language import and export it. If you're moving data from one system to another, CSV is almost always accepted.
XLSX is the standard for people working in spreadsheets. Excel, Google Sheets, Numbers and LibreOffice all open it, and libraries exist for most languages, but it's more complex to generate and parse than CSV.
Common CSV pitfalls
Because CSV has no types, Excel guesses when opening it. It may strip leading zeros from ZIP codes and phone numbers, turn long numbers into scientific notation, or convert values like 1-2 into dates. Importing with Data, From Text/CSV lets you set column types to avoid this.
Separators and encoding cause trouble too. In many European countries Excel expects semicolons, and accented characters only display correctly if a UTF-8 CSV starts with a byte order mark. Values containing commas or line breaks must be wrapped in quotes.
Which should you use?
Send XLSX to people who will read and edit the data in a spreadsheet, especially if it has formulas, formatting or several tabs. Use CSV for imports, exports, data feeds, scripts and anything another program will process. If you receive an XLSX and need CSV, export each sheet separately, since CSV holds only one table.
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Questions
Does saving as CSV lose formulas?
Yes. CSV stores only the current values. Formatting, formulas, charts and extra sheets are lost.
Why does Excel remove leading zeros from my CSV?
Excel treats the values as numbers. Import the file with Data, From Text/CSV and set the column to Text.
Is CSV smaller than XLSX?
Often similar. XLSX is compressed, so for large tables it can even be smaller than the CSV.
How do I convert XLSX to CSV?
Use the Excel to CSV tool on this site, which exports every sheet as its own CSV without uploading the file.