A CSV export full of reference numbers
Convert rather than opening the CSV directly. Order numbers and postcodes with leading zeros survive, which is the entire reason to take this route.
Use CSV to XLSX
Turns CSV into a real .xlsx workbook in this tab. Nothing is uploaded, and the file opens in Excel, LibreOffice, Numbers and Google Sheets.
Every value is written as text, on purposeThis is the opposite of what happens when you open a CSV in Excel directly, where 0123 becomes 123 and a long account number turns into scientific notation. Writing text preserves what you had; format the columns yourself afterwards if you want them numeric.
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Browse all developer and data toolsAbout CSV to XLSX
The obvious way to get a CSV into Excel is to double-click it, and that is precisely where data goes wrong. Excel guesses a type for every field as it reads, and its guesses are confident and destructive: a product code of 0123 loses its zero, a sixteen-digit card or account number becomes rounded scientific notation, a value like 1-2 is silently reinterpreted as a date, and in some locales a decimal comma is read as a thousands separator. None of that is recoverable once the file is saved. This converter builds the workbook itself and writes every field as text, so what you had is what you open. Formatting a column as numeric afterwards is one click; recovering a truncated account number is not possible at all.
Work through the input
- The CSV is parsed with the same parser the rest of this site uses, so quoted fields, embedded commas and line breaks inside cells are handled consistently.
- The delimiter is detected automatically, which covers the semicolon-separated files that spreadsheet software produces in much of Europe.
- Short rows are padded so the sheet is a clean rectangle. A ragged row would otherwise look like missing data in a grid.
- The workbook is assembled directly as the ZIP of XML parts that .xlsx actually is, in this tab, with no spreadsheet library downloaded first.
- Values are written as inline text rather than typed cells, which is the step that stops any of the automatic conversions Excel would otherwise apply.
When csv to xlsx is useful
Sending data to someone who only uses Excel
An .xlsx opens cleanly with no import dialog and no locale-dependent delimiter guessing, which is what usually goes wrong when a CSV is emailed between countries.
Check the output
- Everything arrives as text, including genuine numbers. Sums and formulas over those columns will not work until you format them as numeric in the spreadsheet, which is a deliberate trade: it is reversible, and the corruption it prevents is not.
- One CSV becomes one sheet. Combining several files into a single workbook of multiple tabs is not offered here.
- There is no styling. No column widths, colours, frozen panes or filters - a CSV carries none of that, so none can be invented.
- Formulas are not created. A cell containing text that begins with an equals sign stays text rather than becoming a live formula.
- The sheet name is limited to 31 characters and cannot contain the characters Excel forbids; anything invalid is replaced rather than producing a file Excel calls corrupt.
Questions about CSV to XLSX
Why are my numbers stored as text?
Because typing them means guessing, and Excel's guesses destroy leading zeros and long identifiers. Select the column and format it as a number if you need arithmetic; that step is reversible and the data loss is not.
Is this different from just renaming the file?
Completely. A renamed .csv is still comma-separated text. This builds a genuine .xlsx, which is a ZIP archive of XML parts, so it opens without an import step.
Can I put several CSVs into one workbook?
Not currently. Each conversion produces a single-sheet workbook.
Will it handle semicolon-separated files?
Yes. The delimiter is detected from the content, which covers the semicolon convention common across Europe.
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