CSV to Excel Converter that Keeps Leading Zeros
Convert CSV files to a real .xlsx workbook with leading zeros and long IDs kept as text
Drop files here or browse
.csv / .tsv / .txt — read locally, never uploaded
Why double-clicking a CSV in Excel goes wrong
A CSV file has no types, no encoding marker and no agreed delimiter, so when Excel opens one it guesses — and the guesses are destructive. A ZIP code like 02134 becomes 2134, an order ID such as 00417 loses its zeros, a 16-digit card or tracking number is rounded to 15 significant digits and displayed as 4.11111E+15, and a value like 3-4 can turn into a date. If your Windows region uses a decimal comma, Excel expects semicolons, so a comma-separated file lands in a single column. None of that is reversible once you save.
This converter builds a real .xlsx workbook instead, so the type of every cell is decided up front and Excel, LibreOffice, Numbers and Google Sheets open it exactly as written. The whole conversion runs in your browser: the CSV is read with the File API, the workbook is assembled in JavaScript, and nothing is uploaded.
How the conversion decides what is a number
With "Convert numbers" switched on, a value becomes a numeric cell only when it is a plain decimal that survives a round trip: an optional minus sign, digits, an optional fraction and an optional exponent. Anything with a leading zero (007, 02134), more than 15 significant digits (Excel stores numbers as IEEE doubles and silently rounds beyond that), thousands separators, currency symbols or spaces stays text. That is why IDs, phone numbers and postcodes come through intact while prices and quantities stay summable. Switch the option off to write every cell as text, which is the safest choice for data you will only read or re-export.
True and false are kept as text too, so nothing changes meaning silently. Dates are not converted: CSV dates come in too many local formats to guess safely, so they arrive as text you can convert with Excel's Text to Columns or DATEVALUE once you know the format.
Delimiters, quotes, encodings and multiple files
The parser follows RFC 4180. Fields wrapped in double quotes may contain the delimiter, a doubled quote ("") inside a quoted field is a literal quote, and quoted fields may span several lines — a product description with a line break stays one cell rather than breaking the row. Auto-detect tries comma, semicolon, tab and pipe and picks the one that gives a consistent column count; override it if a tiny file is ambiguous. CRLF, LF and old Mac CR line endings are all accepted, and a UTF-8 byte order mark is stripped.
If accented characters look like é after loading a file, it was saved in Windows-1252 rather than UTF-8; switch the encoding and the file is decoded again. Drop several CSV files at once and each one becomes its own sheet, named after the file (trimmed to Excel's 31-character limit, with characters like / and ? replaced), which is handy for monthly exports you want in one workbook. With "First row is a header" on, row one is bold and frozen so it stays visible while you scroll.
How to use the CSV to Excel Converter that Keeps Leading Zeros tool
- 1
Paste or drop your CSV
Paste text or drop one or more .csv, .tsv or .txt files. Each file becomes its own sheet.
- 2
Check the delimiter and encoding
Auto-detect handles comma, semicolon, tab and pipe. Switch to Windows-1252 if accented letters look garbled.
- 3
Choose header and number handling
Keep the header row bold and frozen, and decide whether plain numbers become numeric cells. Leading zeros always stay text.
- 4
Download the .xlsx
Check the preview (numeric cells are green), then download the workbook and open it in Excel, LibreOffice, Numbers or Google Sheets.
Frequently asked questions
Is my CSV uploaded to a server?
No. The file is read and converted entirely in your browser with JavaScript, and the .xlsx is generated locally and handed to you as a download. Nothing is sent to TechLogHub.
Why do my leading zeros disappear when I open a CSV in Excel?
Excel treats anything that looks like a number as a number and drops the zeros. This tool writes values with leading zeros, and numbers longer than 15 digits, as text cells, so 00417 stays 00417 in the workbook.
Can I convert several CSV files into one Excel workbook?
Yes. Select or drop multiple files and each becomes a separate sheet named after its file. Duplicate names get a (2), (3) suffix because Excel requires unique sheet names.
What delimiters are supported?
Comma, semicolon, tab and pipe, detected automatically or chosen manually. Quoted fields containing the delimiter or line breaks are parsed correctly per RFC 4180.
Is there a size limit?
There is no server limit, only your browser's memory. Files of tens of megabytes usually convert in seconds; the preview shows the first 20 rows while the download contains everything up to Excel's 1,048,576-row limit.
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