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Spreadsheet Converter

Convert an .xlsx workbook to CSV, or a .csv file to .xlsx.

How Spreadsheet Converter works

The Spreadsheet Converter reads the OOXML structure of an .xlsx workbook (it is a small zip package under the hood) directly in your browser and writes out one CSV file per worksheet, or does the reverse: turn a .csv file into a single-sheet .xlsx workbook. Nothing goes through a server in either direction.

The scope is honest and deliberately limited to what a browser tab can do reliably: cell values and text are read and written, but formulas, cell styles, number formats and merged cells are not. A cell holding an Excel date serial number is shown as that raw number rather than a calendar date, since converting it correctly requires the cell's number format, which this tool does not parse.

Written by Bastien Sulyan

How to use Spreadsheet Converter, step by step

  1. Drop an .xlsx file to convert it to CSV, or a .csv file to convert it to .xlsx.
  2. For an .xlsx with several worksheets, one CSV file is produced per sheet, named after the sheet.
  3. For a .csv file, the delimiter (comma, semicolon or tab) is detected automatically from the first line.
  4. Download the converted file(s).

Common use cases

  • Extracting a single worksheet from a shared .xlsx report as plain CSV for a script or database import.
  • Turning a CSV export from another tool into a proper .xlsx file that opens cleanly in Excel or Sheets.
  • Converting each sheet of a multi-tab workbook into separate CSV files in one pass.

Frequently asked questions

Are formulas preserved when converting an .xlsx to CSV?

No. Only the cell's displayed value is read, not the formula that produced it. A formula cell exports its last calculated result as plain text or a number, exactly like most spreadsheet CSV exports behave.

What happens to cell styles, colors and number formats?

They are not read or reproduced. The converter only handles the raw value and text content of each cell, in both directions, so a CSV round-tripped to .xlsx will not carry back any formatting.

Why does a date show up as a number like 45292?

Excel stores dates internally as a serial day count. Reading that correctly as a calendar date requires the cell's number format, which this tool does not parse, so it honestly shows the raw stored number instead of guessing.

How is the CSV delimiter chosen?

When converting a .csv to .xlsx, the delimiter is detected automatically by counting commas, semicolons and tabs on the first line and picking the most common one. When converting .xlsx to CSV, the output always uses a comma.

Is my spreadsheet uploaded anywhere?

No. The file is unzipped (for .xlsx) or parsed (for .csv) and rebuilt entirely with JavaScript in your browser tab. No network request is made with your data.