CSV to Excel (XLSX) Converter
Opening a CSV in Excel is where data goes to get quietly changed. A product code of 007 becomes 7, a sixteen-digit order number turns into 1.23457E+15, and a gene name like SEPT1 is helpfully rewritten as 1-Sep. None of it is reversible once the file is saved, and nothing warns you it happened. This converter writes a real .xlsx workbook instead, and by default every field is stored as text, so what you typed is what the cell holds. The header row is bolded and frozen, columns are sized to their contents, and the sheet is named for you. If you do want real numbers and dates, switch to the detect mode: it converts a value only when it survives a round trip unchanged, keeps anything longer than fifteen significant digits as text because that is all Excel can store, and recognises dates only in ISO form rather than guessing whether 03/04 is March or April. The file is built in your browser. Nothing is uploaded, so a spreadsheet of customer records or salaries never leaves your machine.
Text keeps 007, long IDs and codes like SEPT1 exactly as typed. Blue cells in the preview will be stored as numbers or dates.
Paste or drop a CSV to see the preview.
How to use
- Paste your CSV, or drop a .csv or .tsv file.
- Check the delimiter — it is detected for you, but you can force one.
- Leave the cell types on text to keep every value exactly as typed, or switch to detect for real numbers and ISO dates.
- Say whether the first row is a header; it is bolded and frozen if so.
- Name the sheet and download the .xlsx.
Frequently asked questions
- Why does Excel change my data when I open a CSV?
- Excel guesses a type for every field as it reads the file. Leading zeros are dropped because 007 looks like the number 7, long digit strings are shown in scientific notation, and anything that resembles a date is converted to one. Writing a real .xlsx with the cells already typed as text removes the guess.
- What happens to long ID numbers?
- Excel stores only fifteen significant digits, so a sixteen-digit order number or credit-card style reference loses its last digit if it is stored as a number. Anything longer than fifteen digits is kept as text, even in detect mode.
- Why are dates only recognised in ISO form?
- 03/04/2024 is the 3rd of April in most of the world and the 4th of March in the United States. Guessing would silently shift records by a month, so only unambiguous YYYY-MM-DD (optionally with a time) becomes a real date; everything else stays exactly as written.
- Does the header row get frozen?
- Yes. When you mark the first row as a header it is written in bold and the pane is frozen below it, so the column names stay visible while you scroll.
- What about a value that starts with = or +?
- It is written as a text cell, never as a formula, so a field like =1+1 or a phone number starting with + stays literal. That also sidesteps the CSV formula-injection problem, where a crafted field becomes an executable formula on open.
- Is my spreadsheet uploaded anywhere?
- No. The workbook is assembled by your browser and saved straight to your downloads folder. Nothing is sent to a server.
Guides on this topic
Related tools
Excel (XLSX) to CSV, JSON & Markdown
Open an .xlsx workbook in the browser and export any sheet as CSV, JSON or a Markdown table — the file never leaves your device.
CSV Viewer & Sorter
View CSV / TSV data as a sortable, searchable table — open a file or paste rows, no spreadsheet required.
CSV ↔ JSON Converter
Convert CSV to JSON and JSON back to CSV, with a delimiter option.
Spreadsheet Column Converter
Convert between spreadsheet column letters and numbers — A=1, Z=26, AA=27, BC=55 — and between A1 and R1C1 cell notation.
HTML Table to CSV Converter
Extract HTML <table> data into CSV, TSV or semicolon-separated rows, in your browser.
CSV ↔ TSV ↔ Pipe Converter
Switch delimited text between CSV, TSV, pipe, and semicolon — with proper RFC-4180-style quoting and auto-detection.