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CSV to XLSX without losing zeros, dates or accents

Upload the CSV, confirm the detected delimiter and encoding, set column types if needed, then convert and download the XLSX workbook. Leading zeros and long numbers are kept as text.

CSV Encrypted, deleted after conversion

XLS, XLSX, XLSM, XLSB, ODS, CSV, TSV, Numbers, JSON, XML

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Demo converts up to 100 rows, once.

Sheet

Delimiter

Encoding

JSON shape

Minify JSON

SQL dialect

Table name

Wrap in a transaction

Dates

Row element

Orientation

Workbook password (if protected)

Trim spaces in every cell Remove duplicate rows Drop empty columns Stack all sheets into one table

Double clicking a CSV in Excel looks like a conversion, but Excel guesses. It strips leading zeros from ZIP codes, turns 16 digit card or account numbers into 1.23E+15, reads 03/04 as a date and ignores UTF-8 if the file has no byte order mark. The result is often a silently damaged sheet.

XlsConverter detects the delimiter and encoding, lets you set the type of each column, and writes a proper XLSX with a header row, filters and frozen panes. Need the old format for a legacy system? Use CSV to XLS. Working with tab separated files? Try TSV to XLSX.

How to convert CSV to XLSX in three steps

1Upload one CSV or many CSV files at once.
2Check the delimiter, encoding and column types in the preview.
3Convert and download the XLSX, with one sheet per CSV if you like.

How Excel damages CSV data on open and how to avoid it

CSV carries no types, so whatever opens it has to guess. Excel treats anything that looks like a number as a number, which drops the zero from 02134 and rounds a 19 digit order ID because Excel keeps only 15 significant digits. Marking those columns as text before the XLSX is written keeps them exact, and they stay exact when the workbook is opened.

Dates are the second trap. 03/04/2026 is March 4 in the US and April 3 in Europe. We look at the whole column to work out the order (a value like 25/04 settles it) and write real Excel dates, so sorting and filtering work. If your data goes the other way later, XLSX to CSV writes ISO dates that no system misreads.

Encoding problems show up as Ã© instead of é. That happens when a UTF-8 file without a BOM is read as Windows 1252. Our reader checks the byte patterns, so the workbook shows the right characters. For files larger than 1,048,576 rows we split the data across sheets automatically, because that is the XLSX row limit. If the CSV is headed for a database instead, CSV to SQL skips the spreadsheet step entirely.

Options for CSV to XLSX

Delimiter detection: Automatic detection of comma, semicolon, tab or pipe, with manual override.
Encoding: Reads UTF-8, UTF-8 with BOM, UTF-16 and Windows code pages and writes clean Unicode into the workbook.
Column types: Mark columns as text, number or date so codes with leading zeros are never converted to numbers.
Header row: Use the first row as bold, frozen column headings with filters turned on.
Merge into one workbook: Put several CSV files into one XLSX, each on its own named sheet.

Run it automatically

Many systems can only export CSV, while the people who read the data want Excel. A pipeline can pick up every CSV that lands in an inbox, S3 bucket or Dropbox folder, apply saved column types and widths, and deliver a formatted XLSX to the team folder. Set this up in CSV to Excel automation or call the API after your own export job.

CSV to XLSX questions

How do I convert CSV to XLSX and keep leading zeros?

Mark the column as text before converting. The values are then written as text cells, so 00742 stays 00742 in the workbook.

Why does Excel show strange characters when I open a CSV?

The file is UTF-8 without a byte order mark and Excel reads it with your regional code page. Converting to XLSX fixes this because the workbook stores text as Unicode.

Can I combine several CSV files into one Excel workbook?

Yes. Upload them together and choose one workbook, and each CSV becomes a named sheet.

What happens if my CSV has more than 1,048,576 rows?

That is the XLSX row limit, so the data continues on additional sheets with the same header row.

Can I convert CSV to XLSX in a demo?

Yes, once, for up to 100 rows, with the result visible in the browser and downloadable after signup. Complete files require a plan from 24 USD per month billed yearly.

Related converters

CSV to XLS TSV to XLSX XLSX to CSV CSV to JSON CSV to SQL

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