CSV to XLSX Converter
Convert CSV to XLSX in your browser. Get a real Excel-compatible spreadsheet that preserves your data faithfully — numbers stay numbers, text stays text, leading zeros don't get stripped from columns of phone numbers or zip codes. Works in Excel, Google Sheets, Numbers, LibreOffice, and anywhere else .xlsx is accepted.
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Sensitive documents stay private
Resumes, contracts, NDAs, notes you'd never paste into a chatbot — these are the documents most worth keeping off cloud converters. Everything here happens in your browser. The converted file goes straight to your downloads, then it's gone from memory.
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CSV → XLSX done right
Output is a standard .xlsx file with one sheet named "Sheet1". Numbers are detected as numbers and text stays as text. Strings that look like dates (e.g. "2026-01-15") are kept as text, not auto-converted to dates — this avoids the classic Excel-mangled-my-dates frustration. Format them in Excel afterward if you need date types.
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No signup, no watermark, no email
You don't make an account, you don't enter an email, you don't see ads, and the output isn't watermarked. Free in the actual sense of the word — not "free for now, while we figure out a paywall."
Frequently asked questions
Does my file ever leave my device?
No. The conversion runs entirely in your browser. The file is read into memory, processed by a JavaScript library running in the same tab, and the result is delivered straight to your downloads. Open DevTools while you convert — you'll see zero network traffic carrying your file. This matters for anything sensitive: contracts, drafts, financial documents, personal notes.
Is there a file size limit?
No fixed limit. The real ceiling is your device's memory. Most text and PDF files are small enough that this is never a concern — multi-megabyte documents convert fine on phones. Very large files (hundreds of MB) may struggle on older or memory-constrained devices.
What about the original file?
Untouched. The converted file is a separate copy that lands in your downloads. Your original stays exactly where it was on disk.
Does this work on mobile?
Yes. Tap the drop zone to open your phone's file picker, choose a file from Files / Downloads / Drive / iCloud, hit Convert. The result downloads to your device's standard download location.
How is this different from online converter sites that ask for an email?
Those sites upload your file to their servers, run conversion server-side, and email you a download link. They get to read your document, log your IP, and store the file (for some period). This tool does none of that — everything runs in your browser tab. We don't even have an account system, so there's nothing to sign up for and nothing to log out of.
Why convert CSV to XLSX in the first place?
Excel often mangles CSV files when you open them — strips leading zeros from zip codes (08540 → 8540), interprets dates differently than the source intended, converts long numbers to scientific notation (12345678901234 → 1.23E+13), and chokes on UTF-8 characters without a BOM. Converting to a real .xlsx file first locks in cell types and encoding so the data opens correctly in Excel, Google Sheets, Numbers, or anywhere else.
Does it handle quoted fields with commas inside?
Yes — standard RFC-4180 CSV is supported: fields wrapped in double quotes, embedded commas like "Smith, John", escaped quotes like "She said ""hi""". The parser auto-detects the field delimiter (comma, semicolon, or tab) based on what's most common in the first few rows.
What about my dates?
Dates are kept as text by default — not auto-converted to date cells. This is intentional. Excel's date detection is notoriously aggressive and can mangle ISO-formatted strings ("2026-01-15" might become a date in your locale's format, or worse, get misinterpreted as a 2025 date). Open the .xlsx in Excel and apply a date format to the relevant column yourself for precise control.
What if my CSV uses semicolons instead of commas?
European CSVs (especially from German/French/Dutch Excel locales) commonly use semicolons as field delimiters because the comma is reserved for decimal separators. The parser auto-detects this. If detection gets it wrong, the result will look like one long column per row — we'll add an explicit delimiter picker in a future update.
Are there size limits?
Soft limit around 5MB of CSV input — that's roughly 50,000–200,000 rows depending on column count. Above that the browser may take 10+ seconds to build the .xlsx, but it still works. Excel itself caps spreadsheets at 1,048,576 rows, so anything you can fit in a CSV that Excel can open will work here.
Will the output preserve cell formatting (colors, fonts)?
No — CSV has no styling, so we have nothing to preserve. The output is plain unstyled cells. Apply formatting in Excel after conversion.