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CSV to Excel Converter

Turn pasted CSV into a real .xlsx workbook with SheetJS. Cells are written as text, so Excel can't strip leading zeros or turn codes into dates when the file opens.

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Quick answer

Paste CSV and download a genuine .xlsx workbook (Office Open XML), built in your browser with the SheetJS library. It writes the parsed cells as text, so 00123 ZIP codes and product IDs keep their leading zeros. Excel drops those zeros without warning when you double-click a CSV. The catch is that numbers arrive as text too, so convert those columns if you need to calculate with them.

What the CSV to Excel Converter does

Paste comma-separated data, click Download, and you get data.xlsx, a single-sheet Excel workbook built on your device. The box starts with a small example so you can try it straight away.

Renaming a .csv to .xlsx doesn't work; this writes a proper Office Open XML file. Because the cells are stored as text, Excel leaves entries like 00123 or SEPT9 alone when it opens the file.

How it works

The CSV is parsed into rows under the RFC 4180 rules and passed to the SheetJS library as an array of arrays. SheetJS then writes the .xlsx, which is a zipped bundle of XML parts in the Office Open XML format.

Every cell is written as text, so the sheet holds exactly what you pasted. The file downloads as data.xlsx with one sheet named Sheet1.

Data source & conversion logic

No external data. The CSV is read per RFC 4180, then the SheetJS library writes an Office Open XML (.xlsx) workbook in your browser. Nothing is uploaded.

  1. Step 1. Parse the pasted CSV into rows, handling RFC 4180 quoting.
  2. Step 2. Pass the rows to SheetJS as an array of arrays.
  3. Step 3. Write each cell as text so values keep their original form.
  4. Step 4. Build a one-sheet workbook (Sheet1) in the Office Open XML format.
  5. Step 5. Download it as data.xlsx.

Privacy

SheetJS builds the workbook in your browser, and the data is never uploaded.

The file is generated when you click and the page keeps no copy of it.

You can use it on confidential data such as payroll or customer records.

Technical details

InputCSV text
Output.xlsx (Office Open XML), one sheet
EngineSheetJS (loaded on demand)
Cell typeText, so leading zeros stay
Sheet nameSheet1
Downloaddata.xlsx
Where it runsIn your browser; nothing is uploaded

Standards and references

  • RFC 4180: the CSV rules the parser follows before the workbook is built.
  • Office Open XML / .xlsx (ECMA-376, ISO/IEC 29500): the standard zipped-XML workbook format the tool writes. Excel, Google Sheets and LibreOffice all read it.
  • SheetJS: the in-browser library that writes the .xlsx file.

Accuracy and limits

Numbers come in as text cells. That is on purpose, because it protects ZIP codes and IDs, but Excel may flag them as 'number stored as text', and you'll need to convert a column before doing arithmetic on it.

It writes one sheet named Sheet1, with no extra tabs, formulas or formatting.

It expects comma-delimited input with RFC 4180 quoting. Convert semicolon- or tab-separated data first.

The output is a real .xlsx, not a renamed CSV, so it opens cleanly in Excel, Google Sheets and LibreOffice.

Real-world uses

Send a proper Excel file

Give a colleague an .xlsx instead of a raw CSV that Excel might mangle on open.

Protect codes and IDs

Keep ZIP codes, SKUs, phone numbers and account numbers that Excel would otherwise cut short or reformat.

Meet an upload requirement

Produce the .xlsx that some upload forms and processes insist on.

Spreadsheet from pasted data

Make a clean one-sheet workbook from data you copied from somewhere else.

When it fits, and when it doesn't

Good for

  • A real .xlsx built from CSV
  • Keeping leading zeros and codes intact
  • Sharing a file in Excel's own format
  • A quick single-sheet workbook

Not the best choice for

  • Multi-sheet workbooks
  • Formulas or cell formatting
  • Numbers you need to calculate with straight away

If you need to calculate right away, convert the text columns in Excel or keep the data as CSV. Multiple sheets and formulas are easier to build in Excel itself, and plain CSV is simpler when you only need portable text.

Frequently asked questions

Is this a real .xlsx or just a renamed CSV?
A real one. SheetJS builds an Office Open XML workbook (a zipped set of XML parts), so it opens in Excel, Google Sheets and LibreOffice. A CSV with its extension changed does not.
Why are my numbers stored as text?
To protect values like 00123 and SEPT9 that Excel would otherwise rewrite. Writing every cell as text keeps your data exactly as pasted, but numeric columns need converting before you calculate with them.
Does it keep leading zeros on ZIP codes and IDs?
Yes, and that is the main reason to use it. The cells are text, so 00123 stays 00123. When Excel opens a CSV directly it becomes 123.
Will the file open in Google Sheets or LibreOffice?
Yes. Office Open XML is a published standard (ECMA-376 / ISO/IEC 29500), and any modern spreadsheet app reads it.
How many sheets does it create?
One, named Sheet1. For several tabs, build the workbook in Excel.
Is my data uploaded?
No. SheetJS runs in your browser and the workbook is put together on your device. Nothing goes to a server.
What delimiter does my CSV need?
A comma. Convert semicolon- or tab-separated data to comma-separated CSV first.
How do I turn the text numbers back into real numbers?
In Excel, select the column and use Convert to Number (or Data → Text to Columns), or paste-special multiply by 1. Do this only on columns where leading zeros don't matter.
Why is opening a CSV directly in Excel risky?
Excel scans the first rows and guesses a type for each column. It strips leading zeros, turns codes like SEPT9 into dates and shows long digit strings in scientific notation. An .xlsx with text cells avoids all of that.
Does it handle quoted fields with commas?
Yes. The CSV is parsed per RFC 4180, so a comma inside a quoted field stays part of that cell.
What's the file named, and can I rename it?
It downloads as data.xlsx. Rename it afterwards to whatever you like.
Does it preserve formatting or formulas?
No. It writes cell values only, without colours, fonts or formulas.

References

The tool writes an Office Open XML workbook with SheetJS and stores cells as text. Leading zeros and codes come through intact, which is not the case when Excel opens a CSV directly.

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