Quick Verdict
Use XLSX when…
Use XLSX for human-facing reports — when the audience will open it in Excel, look at formatted tables, click charts, or interact with formulas. XLSX preserves the full spreadsheet experience.
Use CSV when…
Use CSV for machine-facing data — database imports, API ingestion, data pipelines, BI tools, and anything that needs raw values. CSV is universally readable by every data tool ever built.
XLSX vs CSV: Feature Comparison
| Feature | XLSX | CSV |
|---|---|---|
| Format type | Compressed XML (OOXML) | Plain text |
| Formulas preserved | Yes | No (values only) |
| Multiple sheets | Yes | No (one sheet per file) |
| Formatting | Yes (fonts, colours, borders) | None |
| Database import | Limited | Universal |
| File size (10K rows) | ~500 KB | ~200 KB |
When XLSX wins
- ✓Format type: Compressed XML (OOXML)
- ✓Formulas preserved: Yes
- ✓Multiple sheets: Yes
When CSV wins
- ✓Format type: Plain text
- ✓Formulas preserved: No (values only)
- ✓Multiple sheets: No (one sheet per file)
Frequently asked questions
Will Excel preserve leading zeros in CSV?
By default no — Excel auto-formats CSV cells, often converting '01234' to '1234' (treating as a number). To preserve leading zeros: import via Data → Get External Data → From Text and explicitly set the column as Text. Or save as XLSX with explicit text formatting.
Why are CSV files always smaller than XLSX for the same data?
CSV is pure text with minimal overhead. XLSX is XML wrapped in ZIP — for small datasets, the XML overhead exceeds the size of the data. For very large datasets (millions of rows), XLSX's compression eventually becomes more efficient than uncompressed CSV.
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