CSV or XLSX: which format to use and when
When it's time to export a spreadsheet, the same question always comes up: save as CSV or XLSX? Both store data in a table, but they serve different purposes. Choosing wrong can cost you lost formulas or broken accents. Here's how to decide.
What each format is
CSV (Comma-Separated Values) is a plain text file: each line is a table row, and columns are separated by a delimiter (comma or semicolon). It's simple, lightweight and read by virtually any system.
XLSX is the modern Excel format. Beyond the data, it stores formulas, formatting, multiple sheets, charts and data types (dates, numbers, currency).
When to use CSV
- To import and export data between different systems.
- When the destination is a database, an API or another tool.
- For lightweight files with many rows and no need for formatting.
The limitation: CSV doesn't store formulas, formatting or sheets. It's just the raw data.
When to use XLSX
- When you need formulas, charts or multiple sheets.
- For reports that will be read by people, with visual formatting.
- When data types (dates, currency) must be preserved.
The limitation: bigger files, and not every system imports XLSX easily.
Quick summary
| Criterion | CSV | XLSX | | --- | --- | --- | | Formulas and formatting | No | Yes | | Multiple sheets | No | Yes | | File size | Smaller | Larger | | Cross-system compatibility | Very high | Medium | | Best for | Exchanging data | Reports |
And when it's time to merge?
The source format doesn't matter — what matters is the result. On Tablix you can upload CSV and XLSX files together, pick the columns and download a unified file — without worrying about delimiters or encoding.
Frequently asked questions
Can I convert CSV to XLSX and vice versa? Yes. Excel and most spreadsheet tools open one and save as the other. Remember that saving as CSV loses formulas and formatting.
Which format takes less space? CSV, because it's plain text. For large volumes without formatting, it's lighter.
Which one should I choose to merge spreadsheets? Use the format the destination expects. See how to merge spreadsheets in Excel and how to combine CSV files.