Direct comparison
CSV vs XLSX for Research Data: Which to Use
CSV vs XLSX for research data: standards status, what Excel drops when saving to CSV, row and precision limits, and when to pick each, from primary sources.
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How do CSV, XLSX compare side by side?
The table below compares CSV, XLSX across 13 procurement-relevant dimensions, from standards status through source.
Side-by-side comparison
| Dimension | CSV | XLSX |
|---|---|---|
| Standards status | RFC 4180 documents common practice and registers the MIME type text/csv. It states that it does not specify an Internet standard of any kind, and that no formal CSV specification existed before it. | Standardised as ISO/IEC 29500 and ECMA-376 (Office Open XML). The Library of Congress describes it as an international open standard, very widely used, and the default Excel save format since Excel 2007. |
| How the file is built | Plain text. Each record is on a separate line ended by a line break (CRLF), with fields separated by commas. An optional header line may come first. | A ZIP-style package (Open Packaging Conventions) whose primary content is marked up in SpreadsheetML. |
| Fields with commas, quotes or line breaks | RFC 4180: fields containing line breaks, double quotes or commas should be enclosed in double quotes. | Not delimited text: the primary content is marked up in SpreadsheetML inside the package. |
| Several sheets in one file | No. When a workbook is saved as CSV from Excel, only the current worksheet is saved to the new file. | Yes. The number of sheets in a workbook is limited only by available memory. |
| What is lost when you save to it from Excel | Microsoft warns that some features might be lost when a workbook is saved in CSV format. | This is the default Excel save format (since Excel 2007), so the workbook is saved in its own format. |
| Row, column and cell limits in Excel | Import and export in Excel are limited to 1,048,576 rows and 16,384 columns. | Worksheet size is 1,048,576 rows by 16,384 columns; a cell holds up to 32,767 characters. |
| Numeric precision | RFC 4180 describes records and fields only and defines no numeric types. Once a CSV is opened in Excel, Excel's 15-digit precision applies. | Excel stores numbers to 15 digits of precision. The Library of Congress notes about 15 significant digits as a limitation for datasets. |
| Data types and metadata | No data types are defined by RFC 4180; every value arrives as text for the receiving program to interpret. | The Library of Congress notes no strict data typing and no built-in rich discipline-specific metadata. |
| Automatic conversion when typing in Excel | Applies to whatever is typed or opened in Excel, not to the text file itself. | Excel turns entries such as 12/2 into dates and 1e9 into 1.00E+09, and Microsoft says there is no way to turn the date conversion off. Preformat the cells as Text, or start the entry with an apostrophe. |
| Delimiter and character set | RFC 4180 uses the comma and allows other IANA text character sets through the charset parameter. In Excel the default separator is a comma and can be changed in Windows Region settings. | Not a delimiter question: the content is XML inside the package. |
| Long-term preservation | The Utrecht University geo-data support page (December 2022) recommends CSV or ODS over XLSX for data, calling Excel's formats closed; that is the university's position, and it differs from the Library of Congress description of XLSX as an open standard. | The Library of Congress Recommended Formats Statement lists XLSX as a preferred format for datasets. |
| When to pick it | When the data is one flat table that other software must read as plain text, and you can accept that only one sheet and no workbook features are kept. Utrecht University notes CSV needs uniform column lengths, can have trouble when the delimiter occurs in the data, and is not suited to free-text surveys or cell calculations. | When the work spans several sheets or features that must stay together, or the deposit venue asks for it. Be aware of the 15-digit precision and Excel's automatic date and number conversion for anything typed in. |
| Source | IETF RFC 4180; Microsoft Support, Import or export text (.txt or .csv) files; Utrecht University geo-data support (read 2026-10-29). | Library of Congress Digital Formats, XLSX Transitional (fdd000398); Microsoft Support, Excel specifications and limits; Microsoft Support, Stop automatically changing numbers to dates (read 2026-10-29). |
Common questions
Common questions about CSV vs XLSX
Is XLSX a proprietary format?
+
Not in the sense often claimed. The Library of Congress describes XLSX (Office Open XML) as an international open standard under ISO/IEC 29500 and ECMA-376. Utrecht University's geo-data support page nonetheless calls the Excel file formats closed and recommends CSV or ODS; treat that as one institution's guidance.
Is CSV an official standard?
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No. RFC 4180 is an informational document that records common practice and registers the text/csv MIME type. It says it does not specify an Internet standard of any kind.
What happens when I save an Excel workbook as CSV?
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Only the current worksheet is saved to the new file, and Microsoft warns that some features might be lost.
How many rows can Excel open from a CSV file?
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Excel's import and export limit is 1,048,576 rows and 16,384 columns, the same as its worksheet size. A single cell can hold up to 32,767 characters.
Why did Excel change my values to dates or scientific notation?
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Excel is preprogrammed to treat entries such as 12/2 as dates and to show 1e9 as 1.00E+09. Microsoft says there is no way to turn off the date conversion; preformat the cells as Text or start the entry with an apostrophe.
