CSV to Excel Converter

How the CSV To Excel Converter works

CSV is the lowest common denominator of data exchange: every database, bank and analytics tool can write it. Excel is where most people actually read it. The trouble is that opening a CSV directly in Excel triggers a series of guesses about encoding, separators and data types, and several of those guesses quietly damage data.

What goes wrong when Excel opens a CSV

• Leading zeros vanish. Postcodes, phone numbers and product codes such as 00742 become 742.
• Long numbers are rounded. Excel keeps 15 significant digits, so a 16-digit card or account number gets its last digit replaced with zero.
• Text turns into dates. Gene names such as MARCH1 and part codes such as 1-2 become dates. This was common enough that the human gene naming committee renamed several genes in 2020.
• Accents break. Without a byte order mark, older Excel versions read UTF-8 as Windows-1252, turning é into é.
• Everything lands in column A. In regions that use a comma as the decimal mark, Excel expects semicolons and leaves comma-separated files unsplit.

How the CSV to Excel converter avoids that

Converting to .xlsx first removes the guessing, because a workbook stores each cell's type explicitly. The converter reads your file as UTF-8, strips any byte order mark and detects the delimiter by checking which of comma, semicolon, tab and pipe splits the first lines most consistently. Files ending in .tsv are always read as tab-separated. Quoted fields follow RFC 4180, so commas, quotes and line breaks inside quotes are kept.

A value is stored as a number only when it is a plain decimal that Excel can hold exactly: an optional minus sign, digits, an optional fraction, no leading zero and at most 15 significant digits. Everything else, including 00742, 1-2, MARCH1, phone numbers with spaces and very long IDs, is stored as text exactly as written. The Cells stored as numbers reading tells you how many cells will add up in a formula.

Excel caps a sheet at 1,048,576 rows and 16,384 columns, and a cell at 32,767 characters. Files over the row or column limit are refused, and longer cells are cut to fit with a note saying how many were affected.

Exporting a sheet as CSV

Drop an .xlsx file and choose which sheet to export by its position, counting from 1. The tool reads the stored cell values rather than what is on screen:

• Formulas export their last calculated value, as saved by Excel.
• Dates are stored by Excel as serial numbers. Cells formatted as dates are converted to ISO dates such as 2026-10-01, with times added when present. Workbooks using the 1904 date system, common in older Mac files, are handled.
• Numbers are written at full precision, without currency symbols or thousands separators.
• Text is quoted when it contains the delimiter, quotes or line breaks.

Every row is padded to the same number of columns, and lines end with CRLF as RFC 4180 specifies. The Formulas reading counts how many cells came from formulas, so you know which values will not update if the source data changes.

Delimiter and byte order mark

Comma is the default and suits most software. Pick Semicolon for Excel in much of Europe and South America, where the comma is the decimal mark. Tab produces a .tsv file, which avoids quoting problems when text contains commas.

The UTF-8 byte order mark is three invisible bytes at the start of the file. Excel uses it to recognise UTF-8, so keep it if the CSV will be opened in Excel. Choose No BOM for files headed to scripts, databases or Unix tools, some of which treat the mark as part of the first column name.

Limits

Old .xls files from Excel 2003 and earlier use a different binary format and are not supported; save them as .xlsx first. Password-protected workbooks are encrypted and cannot be read. Only cell values travel between formats, so formatting, charts, comments, merged cells and formulas themselves are not carried over.

Privacy

Spreadsheets often hold payroll, customer lists and financial data. This converter reads and writes files entirely in your browser, so nothing is uploaded, logged or kept on a server.

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