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CSV vs XLSX — when to use which

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Excel’s Save As offers XLSX, CSV, XLS and more. They all seem to hold a table, but they are very different things.

Side by side

CSV XLSX
What it is A text file with comma-separated cells An Excel workbook (a ZIP of XML files)
Sheets One Many
Formatting (colours, fonts, borders) ❌ ✅
Formulas ❌ (values only) ✅
Date and number formats ❌ (stored as text) ✅
Encoding problems Possible (garbled characters) None
Opens in a text editor ✅ ❌
Compatibility with software and databases Almost universal Spreadsheet apps
Size Small Moderate (compressed)

When CSV is the right choice

  • Importing into other systems: online shops, accounting software, databases and email tools almost all import CSV.
  • Programming and analysis: Python, R and SQL tools read it directly.
  • Version control: as plain text, changes are easy to compare in Git.

When XLSX is the right choice

  • Documents people read and edit: formatting, formulas, multiple sheets and charts.
  • Sharing: no encoding issues — it opens the same on every computer.
  • Preserving data exactly: leading zeros and dates aren’t reinterpreted when someone opens the file.

The two classic CSV problems

  1. Garbled characters — a CSV doesn’t record its encoding, so Excel may misread UTF-8. → Fix garbled CSV text in Excel
  2. Disappearing leading zeros — Excel turns codes like 007 into numbers. → Keep leading zeros

Both go away once the data is in XLSX. The CSV to XLSX converter detects the encoding and keeps leading zeros and long IDs exactly as written.

What happens when converting XLSX to CSV

With XLSX to CSV:

  • each sheet becomes its own CSV (several sheets arrive as a ZIP),
  • formulas are replaced by their last calculated values,
  • dates are written as ISO dates such as 2026-01-15, read the same way everywhere,
  • files are UTF-8 with a BOM by default, so Excel shows non-English text correctly when you reopen them.

And XLS?

.xls is the Excel 97–2003 format. It’s limited to 65,536 rows and some newer tools no longer accept it. Converting with XLS to XLSX makes files smaller and more compatible.

Quick decision guide

Situation Format
Sharing a report with colleagues XLSX
Uploading to a shop, database or app CSV (check whether the system wants a BOM)
Developer data, version control CSV or JSON
Long-term archive with formatting XLSX
Long-term archive of raw data CSV

Summary

XLSX for documents people use, CSV for data systems consume. Converting CSVs to XLSX before opening them in Excel avoids garbled text and lost zeros.

Tools used in this guide

CSVXLSXTurn a CSV file into a proper Excel workbook — without losing leading zeros or garbling text.XLSXCSVExport every sheet of an Excel workbook as clean CSV that opens correctly everywhere.XLSXLSXUpgrade old Excel 97–2003 workbooks to the modern XLSX format.CSVJSONTurn CSV rows into JSON, with the header row as keys and numbers typed safely.

Related guides

Excel removes leading zeros from your CSV — how to keep themZIP codes, phone numbers and IDs lose their leading zeros, and long numbers turn into 1.23E+19. Here's why Excel does it and how to keep your data intact.Read guide →Why your CSV shows garbled characters in Excel (and how to fix it)When non-English text in a CSV turns into symbols like "é" in Excel, the file isn't broken — Excel guessed the wrong encoding. Here are three reliable fixes.Read guide →How to open JSON data in ExcelReceived a JSON file from a developer or a service export? Here's how to turn it into an Excel table you can sort, filter and chart — no coding required.Read guide →