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Converting a CSV to Excel without damaging postcodes, decimals or identifiers
CSV is the most widespread exchange format for tables: bank exports, contact lists, extracts from business software, public data. It is a plain text file, one line per row, values separated by a comma or a semicolon. Its simplicity has a downside: it does not say whether “01000” is a number or a postcode, nor whether “1,234” is slightly more than one or more than a thousand. Everything is decided at conversion time, and a wrong reading can distort a table without anyone noticing.
The classic mistakes of a CSV opened in a spreadsheet
A spreadsheet that opens a CSV directly tries to guess the type of each cell, and its choices are known to cause trouble. A postcode such as 01000 loses its leading zero and becomes 1000. A phone number starting with 0 suffers the same fate. An identifier of more than 15 digits, such as an order reference or an account number, is shown in scientific notation, and its last digits are replaced by zeros: Excel keeps only 15 significant digits. Depending on regional settings, some values are also turned into dates.
Once the file is saved, these changes are permanent: the lost zero or digits do not come back. Hence the value of converting the CSV into a real Excel workbook (.xlsx) with explicit rules, rather than letting the spreadsheet guess.
What FileXvert treats as a number
FileXvert applies a cautious rule: a cell only becomes a number when it clearly is one. When in doubt, it stays text, which you can always convert to a number in Excel, whereas a misread number cannot be fixed. We fed the converter typical values; here is what it produces for each.
| Value in the CSV | In the Excel workbook | Reason |
|---|---|---|
| 1234 | number 1234 | unambiguous integer |
| 1234,56 or 1234.56 | number 1234.56 | French or English decimal mark |
| 1 234,56 | number 1234.56 | thousands spaces accepted |
| -12,5 and 0,5 | numbers | sign and leading zero before the decimal mark accepted |
| 1,234 | text “1,234” | ambiguous: 1.234 or 1234 depending on the country |
| 01000 or 0612345678 | text | leading zero: postcode, phone number |
| +33612345678 | text | international phone number |
| 12345678901234567890 | text | more than 15 digits: Excel would round it |
| 12 % or 3,5 € | text | unit or symbol in the cell |
| 2026-10-01 or 01/10/2026 | text | date left as it is |
| 1.234.567 | text | ambiguous thousands separator |
Dates and amounts with a symbol deliberately stay text: their format depends too much on the country to be guessed safely. In Excel, the “Text to Columns” command on the Data tab turns them into real values in a few clicks, specifying the expected format.
Separator and encoding, detected automatically
A French CSV often uses semicolons, since the comma is already the decimal mark; an English-language CSV uses commas. Some software uses tabs or the vertical bar. FileXvert tries these four separators on the first lines of the file and keeps the one that gives regular lines, with the same number of columns. Quotes are respected: a quoted cell “Smith, John” stays a single cell.
Encoding matters too. Recent files are in UTF-8, but older versions of Excel save their CSVs in the Windows-1252 encoding. Read as UTF-8, such a file turns “Orléans” into “Orl�ans”. FileXvert first reads the file as UTF-8 and, if it is not, reads it again as Windows-1252: accents are preserved either way.
What the resulting workbook contains
The result is a one-sheet Excel workbook, named after the file, containing the CSV's values: numbers usable in formulas when unambiguous, text otherwise. It contains no formatting, column widths or formulas: a CSV carries none. The conversion happens in your browser, which matters for a bank export or a customer list.
- Before converting, open the CSV in a text editor to spot the separator and how numbers are written.
- After converting, check a postcode column and an amount column: the former must keep their zero, the latter must be right-aligned, a sign that Excel treats them as numbers.
- To pass the table to someone without a spreadsheet, FileXvert can also convert the CSV straight to PDF.