CSV to XLSX Converter

Convert CSV files to Excel XLSX format. Auto-detects delimiters, infers column types (dates, numbers), and applies header formatting. Batch support.

Drop CSV files here

or click to select · up to 20 files · max 50 MB each

csv

Files never leave your device — processed locally in your browser

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What it does

Auto-delimiter detection

Automatically detects whether your CSV uses commas, semicolons, or tabs as the field separator.

Column type inference

Numbers and dates in CSV are detected and stored as proper Excel numeric/date types, not plain text.

Header formatting

Option to bold the first row (treating it as a header) for cleaner Excel presentation.

Auto-sized columns

Column widths are set based on the longest value in each column for a clean, readable output.

Batch processing

Convert multiple CSV files to XLSX at once.

How to use CSV to XLSX Converter

  1. 1
    Upload CSV files

    Drop .csv files onto the drop zone.

  2. 2
    Set options

    Choose delimiter (or use auto-detect), toggle header formatting and column type inference.

  3. 3
    Convert and download

    Click "Convert to XLSX" and download your Excel file.

When to use this

Sharing data exports with non-technical users

Database and API exports are CSV. Convert to XLSX for sharing with business users who prefer Excel.

Adding Excel features to raw data

Once in XLSX format, add formulas, pivot tables, charts, and filters to your CSV data.

Finance and accounting workflows

Finance teams work in Excel. Convert data exports from accounting software CSV to XLSX for Excel-based analysis.

Common errors & fixes

Data in wrong columns
The auto-delimiter detection may have chosen incorrectly. Manually select the correct delimiter from the options.
Numbers formatted as text
Disable column type inference if you want all values preserved as text strings, or ensure your CSV numbers don't have formatting characters like dollar signs.
Dates appear as serial numbers
Enable "column type inference" to detect date patterns and store them as Excel date values.

Technical details

Input formatCSV (RFC 4180, any common delimiter)
Output formatXLSX (Office Open XML)
LibrarySheetJS (xlsx)
Type inferenceNumbers, ISO dates, and common date formats
Processing locationBrowser (client-side only)

What is CSV?

CSV (Comma-Separated Values) is a flat-text tabular format — simple, universal, and supported everywhere. Every database, programming language, and data tool can read CSV natively. The trade-off is that CSV has no concept of data types, formulas, or formatting — everything is stored as text.

What is XLSX?

XLSX is the Excel 2007+ format stored as a ZIP archive of XML files. Unlike CSV, XLSX supports multiple worksheets, formulas, charts, pivot tables, data types, and rich formatting. XLSX is the standard for business data analysis and reporting.

Why convert CSV to XLSX?

CSV to XLSX conversion adds spreadsheet power to plain data. Once your data is in XLSX, you can add SUM/AVERAGE formulas, apply conditional formatting, create pivot tables, build charts, use auto-filter, and apply cell formats like currency and percentage.

For data that will be used by business users in Excel, XLSX is always a better delivery format than CSV.

Frequently Asked Questions

What is a CSV file?

CSV (Comma-Separated Values) is a plain text format for tabular data. Each line is a row; fields are separated by commas (or another delimiter). CSV has no formatting, formulas, or multiple sheets.

How do I convert CSV to XLSX?

Upload your .csv file, choose options (header formatting, type inference), and click "Convert to XLSX".

Is this CSV to XLSX converter free?

Yes, completely free.

Does the converter upload my files?

No — SheetJS processes everything in your browser.

Can I batch convert multiple CSV files?

Yes, up to 20 files at once.

Will numbers be stored as numbers in Excel?

Yes, if "column type inference" is enabled (the default). Numbers are stored as Excel numeric values, not text.

What is the maximum file size?

No enforced limit. Very large CSV files (100K+ rows) may take a few seconds.

Does it work offline?

Yes, after the first page load.

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