CSV to XLSX Converter with Private Browser Processing
Convert a CSV file into a modern Excel XLSX workbook without uploading it. Preview the parsed table, detect the delimiter, preserve text such as product IDs and ZIP codes, then download a formatted spreadsheet.
Parsed and converted locally. The CSV never leaves this browser.
Excel preview
Add CSV data to inspect rows and columns
How to convert CSV to XLSX online
Choose a CSV file, verify the detected columns, and create an Excel workbook on this device.
Choose a CSV file
Select or drop one .csv file up to 25 MB. The browser reads the file locally using UTF-8 or Windows-1252 encoding.
Check the Excel preview
Confirm that commas, semicolons, tabs, or pipes produce the expected rows and columns. Change the delimiter if automatic detection is wrong.
Download the XLSX workbook
Select Download XLSX to create a formatted workbook with optional headers, filters, frozen first row, and readable column widths.
CSV to XLSX conversion settings
These controls handle the CSV variations most likely to put data in the wrong Excel columns.
| Control | Setting | Effect |
|---|---|---|
| Delimiter | Auto, comma, semicolon, tab, or pipe | Separates each CSV record into the correct Excel columns |
| Encoding | UTF-8 or Windows-1252 | Keeps accented letters and international text readable |
| First row | Optional headers | Styles and freezes the first row and enables Excel filters |
| Data handling | Text-safe values | Keeps leading zeros and long identifiers instead of applying risky number or date guesses |
| Processing | Local browser | No source file is sent to a conversion server |
CSV vs XLSX: what the conversion changes
CSV is delimited plain text. XLSX is a structured Microsoft Excel workbook that can store formatting, filters, data types, and formulas.
| Characteristic | Source | Output |
|---|---|---|
| File structure | CSV: one plain-text table | XLSX: one Excel workbook worksheet |
| Separators | Comma, semicolon, tab, or pipe | Cells stored directly in rows and columns |
| Formatting | Not supported by CSV | Header style, filters, freeze pane, and column widths added |
| Leading zeros | Present as literal text | Preserved because imported fields remain text |
| Formulas and charts | Not available in CSV | Not invented during conversion; add them later in Excel |
What this private CSV converter does
The output is designed for accurate, portable data rather than guessing at dates or converting identifiers into numbers.
Automatic delimiter detection
The parser compares commas, semicolons, tabs, and pipes across multiple records, including delimiters inside quoted fields.
Quoted and multiline fields
Quoted delimiters, escaped double quotes, and line breaks inside quoted cells are parsed as CSV data rather than new columns or rows.
Private local conversion
ExcelJS creates the XLSX file inside the browser. The source CSV is not uploaded, retained, or shared with a third party.
Honest format limits
CSV cannot contain original Excel formatting, worksheets, formulas, charts, or images, so a converter cannot restore features that are absent from the source.
Related Excel and spreadsheet tools
Use the cleanup workflow for CSV imports, or reverse the conversion when another system requires plain-text CSV.
CSV to Excel Cleaner
Paste or upload CSV, remove blank and duplicate rows, transpose the table, and preview it before download.
Open toolXLSX to CSV
Export one worksheet from an Excel workbook as comma-, semicolon-, or tab-delimited text.
Open toolJSON to XLSX
Turn structured JSON records into an editable Excel workbook.
Open toolCSV to XLSX converter FAQ
How do I convert CSV to XLSX?
Choose a CSV file above, check the preview and delimiter, then select Download XLSX. The workbook is created locally and downloads as an .xlsx file.
Is this CSV to XLSX converter free?
Yes. It converts one CSV file up to 25 MB without an account or paid plan.
Is my CSV uploaded to a server?
No. File decoding, CSV parsing, preview, cleanup, and XLSX creation run locally in your browser. The source data does not leave your device.
Does CSV to XLSX preserve leading zeros?
Yes. Fields are written as text by default, so values such as 00123, ZIP codes, SKUs, phone numbers, and long account IDs keep their original characters.
Can it detect semicolon or tab-separated CSV files?
Yes. Automatic detection checks comma, semicolon, tab, and pipe delimiters. You can override the result before downloading.
Which CSV encoding should I choose?
Use UTF-8 for modern exports and international text. Choose Windows-1252 for older Western European files created by legacy Windows applications.
Why does the XLSX file not contain formulas or charts?
CSV stores only plain cell values separated into rows and columns. It has no formulas, formatting, multiple sheets, charts, images, or macros to transfer.
Can Excel, Google Sheets, LibreOffice, and Numbers open the result?
Yes. The generated Office Open XML .xlsx workbook is compatible with current Excel, Google Sheets, LibreOffice Calc, and Apple Numbers.
What happens to duplicate or empty rows?
They are preserved by default on this exact-format converter. Enable the cleanup controls to remove them, or use the CSV to Excel Cleaner for a paste-and-clean workflow.
Can I convert a 25 MB CSV with millions of rows?
The upload limit is 25 MB, but Excel worksheets also have a hard limit of 1,048,576 rows and 16,384 columns. Very large data sets should be split before conversion.
Create a private XLSX workbook
Choose a CSV, verify the parsed columns, and download an Excel-ready workbook without uploading the data.
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