What is the difference between CSV and XLSX?

CSV is a plain-text table format: one row per line, fields separated by commas, usually with a header row. It is the most widely supported data format there is, readable by every spreadsheet, database and analytics tool. XLSX is the standard Excel workbook format: a ZIP archive of XML files describing sheets, cells, formulas and formatting. It has been the Excel default since 2007 and is readable by Google Sheets, LibreOffice and Numbers.

Will I lose anything converting CSV to XLSX?

No. Both formats represent the same data model, so the values and their structure come across intact. Converting XLSX to CSV keeps one sheet only, and exports the computed values rather than the formulas that produced them.

Anything to watch out for with XLSX?

Converting XLSX to CSV keeps one sheet only, and exports the computed values rather than the formulas that produced them. Cell formatting, colours, merged cells and charts have no CSV equivalent and are dropped.

What happens to formulas?

Formulas are carried across between workbook formats.

What if my workbook has multiple sheets?

All sheets are preserved — both formats are multi-sheet containers.

What should I know about starting from CSV?

CSV has no formal specification, only a convention (RFC 4180). Delimiters, quoting and line endings vary between producers. More broadly: CSV is the lowest common denominator of tabular data: one record per line, fields separated by commas, an optional header row. Every spreadsheet application, database and analytics tool reads it.

When is XLSX the right choice?

XLSX suits: workbooks with multiple sheets or formulas; anything a colleague will open in Excel; preserving cell formatting and number formats. It is the wrong choice when programmatic ingestion, where CSV or JSON is simpler to parse.

Is there a file size limit?

No hard limit — the constraint is your browser's memory. Files under 50MB convert in a few seconds. Larger files work but take longer, and a browser tab typically has 250-500MB to play with, so very large batches are better split into smaller groups.

Does this work on mobile?

Yes. The drop zone falls back to your phone's file picker, and the conversion runs on-device exactly as it does on desktop. Large files are slower on a phone because there is less CPU and memory available, but nothing about the workflow changes.

Convert CSV to XLSX

Turn a CSV file into a proper XLSX workbook you can format, sort and hand to a colleague. Free, in your browser, no upload.

Drop spreadsheet files to convert

XLSX, XLS, ODS, CSV

Files stay on your device. Open DevTools' Network tab to verify.

Overview

Why convert CSV to XLSX

XLSX is more compact and carries real type information, which CSV does not. Converting XLSX to CSV keeps one sheet only, and exports the computed values rather than the formulas that produced them.

Comparison

CSV vs XLSX: what actually differs

CSV compared with XLSX across encoding, fidelity, file size and support.
Attribute	CSV	XLSX
Full name	Comma-Separated Values	Office Open XML Workbook
Encoding	Text — editor-readable	Binary
What it preserves	Flat only — no nesting, no types, no formatting	Full — multiple sheets, formulas, formatting, charts
Typical size	Very compact for tabular data	Compact for what it carries; the container is ZIP-compressed
Support	Universal. Every spreadsheet, database and BI tool imports it.	Excel, Google Sheets, LibreOffice, Numbers, and most BI tools.

How to

How to convert CSV to XLSX

01
Drop your CSV file
Drag one or more CSV files onto the drop zone above, or click to browse. Files stay on your device — there is no upload step.
02
Convert to XLSX
convert.now parses the CSV and writes it out as XLSX in a Web Worker, so the page stays responsive even on large files. Nothing is sent anywhere.
03
Download the result
Download the XLSX file, or a zip of all of them for a batch. Filenames are preserved, with the extension changed to .xlsx.

Why here

Why convert.now

Private
Files stay in your browser. No upload step. Nothing for anyone to see.
Fast
No queue, no upload wait. Conversion starts the moment you drop a file.
Free
No ads. No file-count limit. No sign-up wall. Just the converter.

FAQ

CSV to XLSX: common questions

No. The CSV to XLSX conversion runs entirely in your browser. Files never leave your device, and there is no server involved in the conversion at all. Open DevTools' Network tab and run a conversion if you want to confirm it — you will see the page and its code load, and no request carrying your file.

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Last updated 27 August 2026

Why convert CSV to XLSX

CSV vs XLSX: what actually differs

How to convert CSV to XLSX

Drop your CSV file

Convert to XLSX

Download the result

Why convert.now

CSV to XLSX: common questions

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