Why convert CSV to XLSX
Opening a CSV directly in Excel often goes wrong in small ways: ZIP codes lose their leading zeros, long IDs turn into scientific notation, and accented characters appear garbled. Sending a CSV to a client also looks less finished than a real workbook.
This converter builds a genuine .xlsx file with SheetJS. It converts plain decimal numbers into numeric cells so you can sum and chart them, keeps anything that would change meaning as a number as text, and sizes each column to its content.
CSV vs XLSX at a glance
| Feature | CSV | XLSX |
|---|---|---|
| Full name | Comma-Separated Values | Excel Open XML Spreadsheet |
| Type | Tabular data | Spreadsheet workbook |
| Introduced | Early 1970s; described by RFC 4180 in 2005 | 2007 (Excel 2007) |
| Created by | No single owner | Microsoft; standardized as ECMA-376 and ISO/IEC 29500 |
| Structure | Flat rows and columns | Several sheets of cells, stored as zipped XML |
| Comments | No | Yes, as cell comments and notes |
| Data types | Text only, no built-in types | Numbers, text, dates, booleans and formulas |
| Best for | Spreadsheet exports and database imports | Spreadsheets with formatting, formulas and several sheets |
| Support | Excel, Google Sheets, databases and every language | Excel, Google Sheets, LibreOffice and Numbers |
| MIME type | text/csv | application/vnd.openxmlformats-officedocument.spreadsheetml.sheet |
How to convert CSV to XLSX
Step 1: Select the CSV
Drop a .csv file with a header row onto the converter.
Step 2: Keep XLSX as the target
Excel (XLSX) is preselected.
Step 3: Convert
The CSV is parsed, values are typed carefully and a workbook with one sheet is written.
Step 4: Open in Excel
Download the .xlsx and open it in Excel, Google Sheets, Numbers or LibreOffice.
What goes into the workbook
Real numeric cells
Values such as 42, -3.5 or 1999.99 become numbers.
Protected text
Leading zeros, numbers over 15 digits, thousands separators and dates stay as written.
Auto column widths
Columns are sized to their longest value, up to a sensible maximum.
Delimiter detection
Comma, semicolon, tab and pipe separated files are all read correctly.
When an XLSX beats a CSV
Client deliverables. Send a clean workbook instead of a raw export.
Preserving IDs. Account numbers and ZIP codes keep their leading zeros.
Excel-only systems. Some upload forms and ERP imports accept XLSX but not CSV.
Further analysis. Start adding formulas, filters and charts right away.
How values are typed
Only unambiguous numbers are converted: an optional minus sign, digits without a leading zero, and an optional decimal part, up to 15 significant digits, which is Excel's precision limit. Everything else is stored as text exactly as it appears in the CSV.
Dates stay as text on purpose. Formats like 03/04/2026 mean different days in different countries, and guessing wrong silently corrupts data. You can convert a date column in Excel with Text to Columns once you know the format.
- 1250 and 3.75 become numbers.
- 00123, 12345678901234567 and 1,250 stay text.
- 2026-09-17 and TRUE stay text.
Workbook layout
The workbook has one sheet named Sheet1. Row 1 holds the column headers from your CSV, and data starts on row 2. Nested JSON-style values are not expected in CSV, so every cell holds a single value.
Formatting such as bold headers, colors or frozen panes is not added. Apply those in Excel in a few clicks, or save the file as a template.
Tips for CSV to Excel
- Save your CSV as UTF-8 so names with accents come through correctly.
- Keep one header row; extra title rows above it become data.
- Convert date text to real dates in Excel once you know the source format.
- Going back? The XLSX to CSV converter exports the first sheet.
CSV to XLSX questions
Will leading zeros be kept?
Yes. Values like 00123 are stored as text, so Excel shows them exactly.
Are numbers stored as numbers?
Plain numbers up to 15 significant digits become numeric cells that you can sum and chart.
Does it convert dates?
No. Dates stay as text to avoid misreading day and month order. Convert them in Excel once you know the format.
Can I convert semicolon CSV files?
Yes, the delimiter is detected automatically.
How many sheets does the file have?
One sheet, named Sheet1.
Is my data uploaded?
No. The workbook is generated in your browser.