CSV to Excel
Make a real .xlsx from one or more CSV files, with zip codes, long ID numbers and codes kept exactly as written instead of mangled by Excel.
Several files become several sheets in one workbook. Or paste below.
Your data is converted on this device. Nothing is uploaded.
The data Excel quietly changes
Opening a CSV in Excel is the most common way spreadsheets get corrupted, because Excel converts values as it loads them and the file gives it nothing to go on. The damage is predictable: ZIP codes such as 02134 become 2134, product codes like 00045 become 45, long numbers such as tracking or account references are rounded to 15 digits and shown in scientific notation and anything that could be a date is turned into one. Genetics researchers renamed several human genes because Excel kept turning their names into dates.
An .xlsx file can say what each cell is. This tool writes numbers as numbers only when they are unambiguous and everything else as text, so the workbook opens with every value exactly as it appeared in the CSV.
What you get
A standard .xlsx that opens in Excel, Google Sheets, Numbers and LibreOffice. Column widths are set from the content and with a heading row, filter buttons are added to it so the data is ready to sort and filter. Semicolon and tab separated files are detected automatically.
Before and after
The report above the preview counts the values that were kept as text where Excel would have changed them. If it is zero, opening the CSV directly would probably have been fine. If it isn’t, those are the values that would have gone wrong.
Common questions
Why not just open the CSV in Excel?
Because Excel guesses the type of every value as it opens a CSV and the guesses destroy data. Zip codes lose their leading zero, 16-digit account and card references turn into 1.23457E+15 with the last digits replaced by zeros and values like 3-4 or MARCH1 become dates. Once the file is saved, the originals are gone.
Which values become numbers?
Only plain numbers that Excel can hold exactly: no leading zero, no more than 15 significant digits, an optional minus sign and decimal point. Everything else is stored as text, exactly as written, so nothing is reinterpreted. Sums and sorting work on the real numbers as normal.
What about dates?
Dates written year first, such as 2026-09-21, become real Excel dates, because that form can’t be misread. Dates like 03/04/2026 are left as text, since whether that is March or April depends on where the file came from and guessing wrong silently is worse than not guessing.
Can I combine several CSVs into one workbook?
Yes. Choose several files and each becomes its own sheet, named after the file. To stack them into one table instead, use the CSV merge tool first.
Is there a row limit?
Excel itself stops at 1,048,576 rows per sheet. A CSV bigger than that can’t be opened in Excel however it is converted; split it first so each part fits.
Guides
The other tools
All of them work the same way: the file is read in your browser and never uploaded.