Convert CSV to XLSX (Excel)
Turn a .csv file into a genuine .xlsx Excel workbook — built from scratch as a real ZIP+XML file right in your browser, not a renamed CSV. Opens natively in Excel, Google Sheets and Numbers. Nothing is uploaded.
Convert a CSV File to XLSX
Drop a .csv file below. It's parsed with the same delimiter-detection and quote-aware logic as our CSV viewer tool, then written into a genuine Excel workbook structure — previewed here, and ready to download.
🔒 Nothing is uploaded — your file never leaves this deviceOn this page
How this tool builds a real .xlsx workbook
A lot of "CSV to Excel" tools online just rename the file, or generate an old, deprecated binary format. This one actually constructs a valid, modern .xlsx workbook from scratch:
- A real ZIP archive — .xlsx is a ZIP file under the hood. This tool writes proper local file headers, a central directory and an end-of-central-directory record, with a correct CRC-32 checksum for every entry — the same structure our XLSX viewer tool reads on the way in.
- The required OOXML XML parts —
[Content_Types].xml, the package relationships,xl/workbook.xmland a worksheet XML part following the SpreadsheetML schema, written directly per the specification. - Type-aware cells — a value is written as a numeric cell only when it round-trips cleanly as a plain number; anything ambiguous (a leading-zero code, a locale-formatted number) stays text, unchanged.
We test this by generating a workbook, then verifying it independently with Python's openpyxl and a real LibreOffice conversion — not just by eyeballing that Excel doesn't complain.
Why convert CSV to XLSX
CSV can't hold multiple sheets, formulas, cell formatting or column widths. If you're about to build any of that on top of a plain CSV export — or a colleague specifically needs an actual .xlsx file rather than plain text — converting first gives you a real starting workbook instead of formatting it manually after opening the CSV in Excel each time.
Edge cases this tool handles
Values that look numeric but shouldn't be treated as numbers
A leading-zero code like "007" or a phone number is kept as text, not silently converted to the number 7.
Fields containing quotes, commas or line breaks
Parsed correctly from the source CSV (RFC 4180 rules) before being written into the workbook, so nothing is corrupted on the way in.
Non-ASCII characters
Written correctly as UTF-8 throughout the XML, so accented characters, non-Latin scripts and symbols come through intact.
Semicolon or tab-delimited CSV
Detected automatically before conversion, same as the site's CSV viewer tool.
Frequently asked questions
Does converting CSV to XLSX upload my file anywhere?
No. Both the parsing and the .xlsx file construction happen entirely inside your browser using JavaScript — the file's contents never leave your device.
Is the downloaded file a real .xlsx, or just a CSV renamed with an .xlsx extension?
It's a genuine .xlsx workbook — a real ZIP archive containing the required OOXML SpreadsheetML XML parts (workbook.xml, a worksheet, content-type declarations), built from scratch in your browser. Renaming a .csv file to .xlsx does not work; Excel would refuse to open it or show a format-mismatch warning. This tool actually constructs the correct file structure.
Does the converted file keep number formatting, like values with leading zeros?
A value is only written as a numeric Excel cell when it round-trips cleanly as a plain number. Anything ambiguous — like a leading-zero code ("007") or a locale-formatted number ("1.234,56") — is kept as text, exactly as it appeared in the CSV, so your data isn't silently reinterpreted.
Will formulas or formatting be added automatically?
No — the output is a plain data workbook with one sheet, matching what a CSV actually contains. CSV has no concept of formulas or cell formatting, so there's nothing to convert; you get clean data you can then format however you like.
Last updated September 23, 2026.