XLSX to CSV
Convert an Excel .xlsx sheet to CSV in your browser — no upload. Pick the sheet, delimiter, quoting and line ending; dates come out as ISO 8601.
A CSV of the chosen worksheet with values as stored (formula results, TRUE/FALSE, ISO dates), a preview, row/column counts and the file to download.
Example: An orders workbook with two sheets: the Orders sheet (4 × 6) becomes orders-Orders.csv with a date cell written as 2024-03-15 and a multi-line note quoted per RFC 4180.
Values as stored,
one sheet at a time.
How the workbook is read without a spreadsheet library, how each cell type becomes text, and where CSV differs from the sheet.
Reading the workbook
An .xlsx file is a ZIP of XML parts (ECMA-376). The page unzips it in your browser with an in-house inflater, reads the sheet list, the shared-string table and the number-format styles, then walks the chosen sheet's cells. No third-party spreadsheet library is involved and nothing is uploaded.
Cell types
Text and rich-text cells become their plain text; numbers are written as stored (full precision, not as displayed — 0.125 rather than 12.5 %); TRUE/FALSE for booleans; a formula cell contributes its last calculated value; an error cell its code (#DIV/0!). A number whose cell style is a date or time format becomes ISO 8601 — 2024-03-15, 09:05:00 or 2024-03-15T13:30:00 — using the workbook's 1900 or 1904 date system, including Excel's 1900 leap-year quirk.
CSV output
RFC 4180: fields containing the delimiter, quotes, line breaks or leading/trailing spaces are quoted and inner quotes doubled, or every field is quoted if you choose. Trailing empty rows and columns are dropped by default (a leading empty row is kept, since it changes row numbers). Merged cells, formatting, comments and column widths have no CSV equivalent and are not represented. Nothing leaves the browser: the file is read into memory on your device, rewritten there and offered back as a download; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- ECMA-376 Part 1, 5th ed. — Office Open XML SpreadsheetML (sheet data §18.3, number formats §18.8.30, dates §18.17.4)
- RFC 4180 — Common Format and MIME Type for CSV Files (IETF, 2005)
Last reviewed 20 September 2026. How results are checked: How we verify.