CSV to Excel Converter

Convert CSV/TSV files to Excel (.xlsx) format. Files are processed entirely in your browser and never sent to a server.

Tips

  • The sheet in the generated Excel file is always named "Sheet1". If you need multiple sheets, adjust them manually in Excel after downloading.
  • If the source CSV file uses an encoding other than UTF-8 (such as Shift-JIS), the converted text may appear garbled. We recommend re-saving the file as UTF-8 before converting it.
  • After conversion, Excel may automatically interpret cell contents as numbers or dates (for example, "1-2" becomes a date). If you have columns that must keep leading zeros, such as postal codes or product codes, set that column's format to "Text" in Excel after conversion.
  • File contents are processed entirely in your browser (client-side) and are never uploaded to a server, so it's safe to use even with sensitive data.

Frequently Asked Questions

The output is generated in the ".xlsx" format (Office Open XML), compatible with Excel 2007 and later. The older ".xls" format (Excel 97-2003) is not supported.

This isn't a bug in this tool — it happens because Excel automatically guesses a cell's type (number, date, etc.) every time it opens a file. If you need to preserve leading zeros, set the relevant column's format to "Text" in Excel after conversion.

It depends on your browser's memory limits, but files up to a few tens of megabytes typically convert without issues. Very large files may slow your browser down.

Yes. We offer a separate tool dedicated to the opposite direction (Excel to CSV). Use that tool if you want to convert an existing Excel file to CSV.
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Side Note — Why Does Excel "Break" CSV Data?

The problem of Excel silently converting values into dates when you open a CSV file has plagued data engineers worldwide for years. Strings like "1-2" or "3/4" get automatically reinterpreted as dates, with no easy way to recover the original text. Microsoft has been aware of the issue since the 2010s, but backward compatibility has made a proper fix difficult; it wasn't until a 2021 update that Excel finally added the ability to specify a column's type during import.

This problem was most damaging in the field of genomics research. A 2004 study found that roughly 20% of gene name lists published in academic papers had been corrupted by Excel's autocorrection — for example, the gene name "SEPT2" (Septin-2) being converted into "2-Sep" (September 2). In response, the HUGO Gene Nomenclature Committee took the unusual step in 2020 of renaming genes that were especially prone to this kind of corruption.

The ".xlsx" format used by Excel today is actually a ZIP-compressed collection of multiple XML files (Office Open XML, or OOXML). Adopted starting with Office 2007, this format's specification is publicly documented, unlike the older proprietary binary ".xls" format, which makes it far easier for other software to read and write. This open specification is a major reason why open-source libraries like SheetJS — which this tool uses — can generate .xlsx files even without Excel installed.

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