AnyFormat

00 CSV → XLS

CSV to XLS

The legacy binary format, for systems that will not take XLSX.

01CSV in
02XLS out
03Options 4

Exports from European versions of Excel use semicolons, because the comma is the decimal point there.

Off means rows come out as arrays instead of objects.

Off keeps every value as a string — safer for IDs, postcodes and phone numbers with leading zeroes.

  • No upload The conversion runs in this tab. Your file never travels — not to us, and not to the advertising.
  • No sign-up, no email, no daily cap There is no account system to sign up to.
  • No size limit we invented Only your device's memory — about ~2 GB on a desktop browser, ~400 MB on a phone.
  • Turn your Wi-Fi off and convert anyway The conversion needs nothing but this page. Ads will not load without a connection; your file will still convert. That is the whole claim, and it takes five seconds to check.

Produces a genuine legacy .xls workbook. You almost certainly want CSV to XLSX instead — XLS is only the right answer when something downstream refuses anything newer, which in practice means an accounting package, a government upload form or a piece of industrial software.

The 65,536-row wall

XLS cannot hold more than 65,536 rows or 256 columns. That is a hard format limit, not a policy. A larger CSV is refused here with the actual row count so you know by how much — silently truncating at row 65,536 is how people lose the tail of a dataset without noticing.

When XLS is genuinely the right choice

Only when the receiving system says so. Excel 2007 and everything after opens XLS in compatibility mode with a permanent banner, LibreOffice prefers XLSX, and Google Sheets converts it on import anyway. If you have a choice, take XLSX: it is smaller, safer and has none of these limits.

Excel will retype your data unless you stop it

Opening a CSV in Excel is where leading zeros disappear from postcodes, long account numbers become 1.23457E+15, and anything shaped like a date becomes one. The genomics community lost this fight so thoroughly that in 2020 the gene naming committee renamed SEPT1 and MARCH1 — Excel had been turning them into dates for years, in roughly a fifth of published papers with supplementary spreadsheets. Writing a real XLS carries the cell types with it, so text stays text. That is the actual reason to use this rather than renaming the file.

Questions

Should I use XLS or XLSX?
XLSX, unless something specifically requires XLS. XLSX has no practical row limit, compresses far better and is not treated as a legacy format.
My file was rejected for being too large.
XLS stops at 65,536 rows. Use XLSX instead, which allows 1,048,576.
Will Excel complain when it opens the file?
It will open in compatibility mode with a banner, which is normal for the format. It will not warn that the file is corrupt — this is a genuine BIFF8 workbook, not a renamed CSV.
Is my data uploaded anywhere?
No. The conversion runs as JavaScript inside this tab. Open your browser's Network panel and convert something — you will see no request carrying your data, because there is no server to send it to. You can also turn your Wi-Fi off and convert anyway.