CSV to XLS Converter
Turn a comma- or semicolon-separated file into a classic .xls workbook that opens in Excel 97 through today's Microsoft 365. Use it when the system you upload to names the old binary format and refuses anything else.
Data Converter
or drop CSV, TSV, TXT … files here ·
Max 95 MB per file· Up to 20 files· Deleted after 30 minutes
Files are processed on our servers and deleted after 30 minutes.
Character that separates columns in CSV and text files, for both reading and writing. Auto detects it from the input and writes commas.
UTF-8 works for every language. Choose UTF-8 with BOM if Excel on Windows shows garbled accents or Asian characters when opening the CSV.
Excel, ODS and Numbers input: convert the first sheet only, or every sheet (one CSV per sheet in a ZIP, or one JSON key per sheet).
Name of the sheet tab in the new spreadsheet, up to 31 characters.
Array of objects uses column names as keys for every row; array of arrays is more compact and keeps the header as the first array.
Name of the outer element that wraps all rows; each row becomes a <row> inside it.
Used in CREATE TABLE and INSERT statements. Letters, digits and underscores only.
Quoting and column types differ slightly between databases; pick the one you will import into.
Rewrite date cells in one format. ISO (2026-10-18) is safest for databases and code; keep leaves them as they appear in the source.
How to use this tool
- 1
Add your CSV files
Drop one CSV or up to 20 at a time, 95 MB each. Any separator works.
- 2
Confirm how the CSV is read
Delimiter is set to Auto detect. Under Advanced settings you can force Semicolon or Tab, pick the source Text encoding, and rename the tab with Sheet name.
- 3
Convert and upload
Press Convert to XLS, download the workbook and send it to the importer or colleague that asked for the Excel 97–2003 format.
How do I convert CSV to XLS?
Upload the CSV, leave Delimiter on Auto detect and press Convert to XLS. You get an Excel 97–2003 workbook with one sheet, the header in row 1 and every line of the CSV as a row, as long as the file stays within 65,536 rows and 256 columns.
Convert CSV to XLS for systems that only read the old format
People who need a CSV to XLS converter rarely chose the format. An accounting package, a supplier portal or an internal HR tool was built against the binary Excel file that Office 97 introduced, and its upload screen checks the extension. A CSV is refused because it is text; an XLSX is refused because, to that program, it is an unknown ZIP archive.
The conversion itself is simple, because a CSV holds nothing an XLS cannot. Each line becomes a row, each separated value a cell, and the first line becomes the header. What the workbook adds is structure the importer expects: a named sheet, a fixed cell grid and numbers stored as numbers instead of characters. If nothing on your side requires the old type, CSV to XLSX is the better choice, since every current spreadsheet app treats XLSX as its default.
XLS file limits to check before converting
- rows per XLS sheet
- 65,536
- columns, A to IV
- 256
- characters in a sheet name
- 31
- per CSV you upload
- 95 MB
The row ceiling is the one that bites. A year of daily transactions from a busy shop, or a customer list exported from a CRM, can pass 65,536 lines easily, and the old format has no way to continue on the same sheet. A CSV with a header and 70,000 records will not fit.
Dates deserve a second look. A CSV stores 03/04/2026 as characters, and whether that means March or April depends on who wrote it. Excel files store dates as serial numbers counted from 1900, so the converter has to read the text one way. Set Dates to ISO under Advanced settings if the importer documents a format, or keep them as they are when you only need the file to open.
How XLS turned into the legacy Excel format
1997
BIFF8 arrives with Excel 97
The binary format behind .xls gains Unicode text and the 65,536-row grid that later versions kept for a decade.
2005
CSV gets a written spec
RFC 4180 documents the comma-separated format that spreadsheets had exchanged informally for years.
2007
XLSX becomes the default
Excel 2007 saves Office Open XML workbooks by default and raises the sheet to 1,048,576 rows and 16,384 columns.
2008
OOXML is an ISO standard
ISO/IEC 29500 is published, and XLS is left as the format older software still reads.
CSV and XLS side by side
CSV
Comma-separated values
CSV is a plain-text format for tables in which each line is a row and commas separate the columns. It has been used since the early days of computing and is described in RFC 4180, though many variants use semicolons or tabs and different text encodings. Nearly every spreadsheet, database and analytics tool can import and export it, which makes it the default format for moving data between systems. CSV stores only values, with no formulas, formatting, multiple sheets or data types.
- Compression
- –
- Transparency
- –
- Animation
- –
- Introduced
- –
XLS
Microsoft Excel 97–2003 workbook
XLS is the binary spreadsheet format used by Excel from Excel 97 until XLSX replaced it in 2007. It is limited to 65,536 rows and 256 columns per sheet and stores data in a proprietary structure. Many legacy systems, government portals and older banking exports still produce or require XLS. Excel, LibreOffice and Google Sheets can open it.
- Compression
- –
- Transparency
- –
- Animation
- –
- Introduced
- 1997 · Microsoft
CSV goes to XLS when the receiving end is frozen in time: a legacy importer, an old Office install or an upload form that only lists the Excel 97–2003 type and turns away both plain text and XLSX.
CSV to XLS questions
Why would anyone still want XLS instead of XLSX?
Because the reader cannot change. In-house import routines written in the 2000s, some government and payroll upload templates, and machines still running Office 2003 parse only the binary BIFF8 file. When an upload form lists .xls as the only accepted type, an XLSX is rejected even though it holds the same rows.
What happens if my CSV has more than 65,536 lines?
An XLS sheet cannot hold them: the format stops at row 65,536, header included. Split the CSV into smaller files first, or produce a modern workbook with CSV to XLSX, which allows 1,048,576 rows per sheet.
Will accented letters and Asian scripts survive in an XLS?
Yes. BIFF8 stores cell text as Unicode, so names in Polish, Greek or Japanese keep their characters. The common problem sits on the input side: if the CSV was saved as Windows-1252 or Shift_JIS, pick that under Text encoding so the converter reads it correctly before writing the workbook.
Can the converter open a semicolon CSV from a European Excel?
Auto detect looks at the first lines and recognizes commas, semicolons, tabs and pipes. A German or French export with semicolons and decimal commas is split into the right columns; set Delimiter by hand only when a file mixes separators.
Is there a column limit as well as a row limit?
Yes, 256 columns, which ends at column IV. Wide exports from analytics tools or survey platforms can exceed that, and columns past IV cannot be stored in the old format.
How do I bring the XLS back to plain CSV later?
Run it through Excel to CSV. Values come back as they were; only the sheet name and cell types are dropped.
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