CONVERT
CSV → XLSX
Tap to choose your fileDRAG. DROP. DONE.
Upload any file and our engines will handle format detection automatically.
Max 25 MB · Free plan · No signup required
Convert to:
Detecting available formats...
Optimize for
Leave empty to use original name. Extension added automatically.
Uploading...
Processing your file...
Import CSV data into a formatted Excel spreadsheet with proper columns and data types.
Converting CSV to XLSX turns a plain-text delimited file into a proper Excel spreadsheet with typed columns, sheet structure, and editing capabilities. Our converter auto-detects the delimiter (comma, semicolon, tab), parses quoted fields correctly, infers column types (number, date, boolean, text), and writes an XLSX that opens instantly in Excel, Google Sheets, Numbers, or LibreOffice Calc.
CSV (Comma-Separated Values)
Source formatCSV is a simple text-based format for tabular data where values are separated by commas. It is the universal interchange format for data between spreadsheet applications, databases, and programming languages.
Excel Spreadsheet
Target formatXLSX is the modern Microsoft Excel format based on Open XML. It is the industry standard for spreadsheets, supporting formulas, charts, pivot tables, and conditional formatting.
Why convert CSV to XLSX
CSV is universal for interchange but strips every feature that makes spreadsheets useful: formulas, formatting, multiple sheets, column types. Converting to XLSX bootstraps the file into a first-class spreadsheet ready for analysis, pivot tables, and charts — no re-importing, no delimiter confusion.
HOW TO CONVERT
CSV → XLSX
Upload the CSV
Drop your .csv file. Delimiter, encoding, and quote style are auto-detected.
Infer and write
Column types are inferred; numbers, dates, and booleans are written as typed cells.
Download the XLSX
Open in Excel or Sheets — columns are sized for visibility and frozen header is applied.
Common Use Cases
Analyst handoff
Data teams export CSV; analysts want XLSX so they can pivot and chart immediately.
Bank statement imports
Banks export CSV; accountants work in XLSX with formatting and formulas.
E-commerce product sheets
Shopify, WooCommerce, and similar export CSV — XLSX is easier for bulk-editing variants.
Survey and form data
Google Forms and Typeform export CSV; XLSX adds charting and conditional formatting.
CSV vs XLSX — Strengths and limitations
What each format does best, and where it falls short.
CSV Strengths
- Universally readable — every spreadsheet, database, and programming language.
- Human-readable in any text editor.
- Stream-friendly — can process terabytes with constant memory.
- Git-friendly — clean diffs of row changes.
- Tiny overhead vs columnar data structures for simple data.
Limitations
- No standard — quoting, escaping, encoding, and separators vary wildly.
- No type information: 0042 might be an integer, a string, or an error.
- Leading zeros and large numbers often get mangled by Excel auto-conversion.
XLSX Strengths
- Much smaller than legacy .xls files thanks to ZIP + XML.
- Human-readable structure — easy to extract data programmatically.
- Supports macros (as .xlsm variant), charts, pivot tables, conditional formatting.
- Universal support: Excel, LibreOffice, Google Sheets, Numbers, pandas.
- ISO/IEC 29500 standardized.
Limitations
- Macros in .xlsm are a common malware vector — disabled by default in Office.
- 1M-row limit is a cultural problem — people put too much data in Excel.
- Subtle formula differences between Excel, LibreOffice, and Sheets.
CSV vs XLSX — Technical specifications
Side-by-side comparison of the technical details.
CSV
- MIME type
- text/csv
- Specification
- RFC 4180 (informational)
- Typical separator
- Comma (;), semicolon, tab, pipe
- Typical encoding
- UTF-8, Windows-1252, ISO-8859-1
- Line endings
- LF (Unix), CRLF (Windows)
XLSX
- MIME type
- application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
- Container
- ZIP (Office Open XML)
- Max rows
- 1,048,576
- Max columns
- 16,384
- Released in
- Microsoft Office 2007
- Variants
- .xlsx, .xlsm (macros), .xlsb (binary)
| Specification | CSV | XLSX |
|---|---|---|
| MIME type | text/csv | application/vnd.openxmlformats-officedocument.spreadsheetml.sheet |
| Specification | RFC 4180 (informational) | — |
| Typical separator | Comma (;), semicolon, tab, pipe | — |
| Typical encoding | UTF-8, Windows-1252, ISO-8859-1 | — |
| Line endings | LF (Unix), CRLF (Windows) | — |
| Container | — | ZIP (Office Open XML) |
| Max rows | — | 1,048,576 |
| Max columns | — | 16,384 |
| Released in | — | Microsoft Office 2007 |
| Variants | — | .xlsx, .xlsm (macros), .xlsb (binary) |
CSV vs XLSX — Typical file sizes
Approximate file sizes for common scenarios.
CSV
- Contact export (1000 rows) 100–300 KB
- Analytics export (100k rows) 10–100 MB
- Large dataset (1M rows) 100 MB – 1 GB
- Full database dump 1 GB – 100 GB
XLSX
- Small budget spreadsheet 20–80 KB
- Financial model with charts 1–10 MB
- Large dataset (100k rows) 10–50 MB
- Enterprise model (1M+ rows) 100–500 MB
Quality & Compatibility
Numeric and date detection uses common patterns (ISO dates, locale-aware numbers). Leading-zero strings (phone numbers, ZIP codes) are preserved as text to avoid Excel reformatting them. No data is altered — only the container changes.
Tips for Best Results
- Include a header row in the CSV — it becomes the frozen top row in the XLSX.
- If your CSV uses semicolons (European locales), the delimiter is auto-detected and handled.
- Leading-zero IDs and phone numbers are preserved as text — no "0055" to "55" conversion.
Frequently Asked Questions
Yes, KaijuConverter auto-detects common delimiters (comma, semicolon, tab) and maps each field to its own Excel column. Numbers, dates, and text are typed correctly.
Yes. The free tier accepts files up to 25 MB without registration, email capture or watermarks; paid plans go up to 2 GB. Paid plans raise the size cap, enable batch conversions and provide a REST API for automation, but nothing on the free tier is quality-limited — the output is exactly the same as on any paid plan.
No. Columns that contain leading zeros (like ZIP codes or phone numbers) are written as text in the XLSX so "00123" stays "00123".
Yes, the free tier handles CSV files up to 25 MB which typically covers hundreds of thousands of rows. For larger datasets, consider our premium plan.
Uploads run over HTTPS, files are processed in isolated containers, and both the source CSV and the XLSX output are auto-deleted within two hours. No account is required, file contents are never logged, and KaijuConverter does not use uploads for AI training. The paid plan adds a signable data-processing agreement for regulated workflows.
Dates in common formats (YYYY-MM-DD, MM/DD/YYYY, DD.MM.YYYY) are detected and written as typed date cells, not strings, so sorting and filtering work correctly.
Yes, KaijuConverter handles UTF-8 encoding by default, so accented characters, CJK text, and special symbols are preserved correctly in the Excel output.
Most files finish in well under a minute. Small images and documents are typically ready in a few seconds; large video or audio files scale roughly with duration. Upload speed from your network is usually the dominant factor, not server time.
Yes. The delimiter is auto-detected per file — comma, semicolon, tab, and pipe are all handled.
The converter streams rows so files up to hundreds of megabytes convert without running out of memory. Excel itself caps at roughly a million rows per sheet.
Related comparisons
See these formats side by side to understand which fits your use case best.
Related Guides
XLSX Format: Inside Microsoft Excel's Open XML Spreadsheet
Complete guide to XLSX format: ZIP+XML structure, shared string table, date serial numbers, cell styles, formula caching, openpyxl programming, pandas integration, and comparison with CSV/ODS.
Read guideCSV and TSV Format: The Complete Technical Guide
Master CSV and TSV: RFC 4180 grammar, proper parsing with csv libraries, encoding pitfalls (UTF-8 BOM), dialect differences, type inference surprises, large-file strategies with DuckDB and Parquet, and conversion to JSON/Excel/SQL.
Read guideCSV Format: The Complete Guide to Comma-Separated Values
Everything about CSV: RFC 4180 specification, delimiter variants, quoting rules, encoding pitfalls, CSV vs TSV vs Excel, and how to convert and fix CSV files.
Read guideSecure & Private Conversion
Your files are encrypted during transfer, processed in isolated containers, and automatically deleted within 60 minutes. We never read, share, or store your data.