How to convert CSV to Excel
- Paste CSV or open a file. Delimiter, encoding and header row are detected automatically.
- Check the cell preview: each value is colored by the type it will have in Excel.
- Name the sheet and the file, then click Download .xlsx.
What each option does
- Numbers as number cells
- So formulas, sorting and charts work. Values Excel would change (leading zeros, more than 15 significant digits) are stored as text with the Text format.
- ISO dates as date cells
- Writes real dates, shown as yyyy-mm-dd (with hh:mm:ss when there is a time). Dates before 1900 stay text because Excel cannot store them.
- Bold and frozen header
- The first row stays visible while you scroll, the way most people set up a sheet by hand.
Column widths are set from the content. The workbook is created with the open-source write-excel-file library, loaded only when you convert.
Frequently asked questions
Why not just open the CSV in Excel?
Excel guesses types when it opens a CSV: it drops leading zeros from ZIP codes and IDs, shows long numbers in scientific notation and can read dates in the wrong order. Converting to .xlsx fixes each cell's type first, so the file opens the same way everywhere.
Which values become numbers or dates?
Plain numbers such as 42, -3.5 or 1e6 become numeric cells. Values with leading zeros or more than 15 significant digits stay text, because Excel would change them. ISO dates and times (2026-10-27 or 2026-10-27 14:30) become date cells; other date styles stay text so nothing is misread.
Is there a size limit?
An Excel sheet holds at most 1,048,576 rows and 16,384 columns, and a cell at most 32,767 characters; longer text is cut and reported. The workbook is built in your browser, so a large file takes a few seconds and some memory.