Convert CSV to XLSX Online — Free

How to convert CSV to XLSX

1. 1

   Add your CSV file

   Drop or select a .csv file. Files up to 50MB process locally in your browser — nothing uploaded.

2. 2

   Run the conversion

   Your CSV is parsed in the browser (auto-detecting comma, tab, or semicolon delimiter), then written as a single-sheet XLSX file via the SheetJS library. Headers become the first row, columns auto-size to content, and values preserve their types (numbers stay numeric, strings stay strings).

3. 3

   Download your XLSX

   One click saves the result as a .xlsx file. Your original file stays on your device.

Why convert CSV to XLSX?

Excel users often prefer XLSX for its formatting capabilities, formulas, multi-sheet support, and charting — all of which CSV can't carry. CSV is a great interchange format but a poor analysis format. Converting to XLSX is usually the first step before a spreadsheet user adds pivot tables, conditional formatting, or formulas on top.

Common CSV to XLSX use cases

• Converting a SQL database export CSV to XLSX for a non-technical colleague who needs pivot tables and charts
• Preparing a Google Analytics or Stripe CSV export for analysis in Excel with formula-based KPIs
• Translating a Python pandas to_csv() output into XLSX for inclusion in a client-deliverable report
• Turning a CRM or HR system CSV export into XLSX for formatting with conditional colors, filters, and freeze panes

What file size to expect

A 5,000-row CSV of 1 MB typically becomes an XLSX of 300-600 KB — XLSX uses ZIP compression internally so it's often smaller than the raw CSV despite the richer format. A 100-row CSV of 10 KB becomes an XLSX of 8-12 KB.

Technical notes: CSV → XLSX

XLSX is a ZIP archive containing XML files (workbook.xml, sheet1.xml, sharedStrings.xml, styles.xml) following the Office Open XML (OOXML) spec. Values are typed during conversion: numeric-looking cells become numbers; quoted numeric strings stay strings (preserves leading zeros like '007'); ISO dates can optionally convert to Excel date serials; true/false strings stay strings by default (Excel typically treats them as text unless explicitly converted). Column widths auto-calculate based on content length. No formatting or formulas are added — the XLSX is a plain tabular conversion.

Compatibility and browser support

XLSX opens in Excel 2007 and later, Google Sheets (via Import), LibreOffice Calc, Apple Numbers, WPS Office, OnlyOffice, Calligra Sheets, and every mainstream spreadsheet app. Pandas reads XLSX via read_excel. It's the most widely-compatible rich spreadsheet format today.

CSV vs XLSX

Frequently Asked Questions