Convert Large CSV to Excel Online — 100MB+ Streaming CSV to XLSX
Convert huge CSV or TSV files to Excel .xlsx directly in your browser — even files over 100 MB. Stream-based processing keeps memory flat, auto-detects encoding (UTF-8, GBK, Shift-JIS, EUC-KR) and delimiters, and keeps long ID columns as text. Files never leave your device. Free for files up to 10 MB; Pro has no size limit.
Click or drag a .csv / .tsv file here
How to convert a large CSV to Excel
- 1. Choose your .csv or .tsv file — encoding and delimiter are detected automatically.
- 2. Pick the output: Excel (.xlsx) or normalized CSV (UTF-8, commas, CRLF).
- 3. Click Convert — the file streams through your browser and downloads when ready.
Key Features
- • Handles files of 100 MB and beyond with a streaming reader
- • Flat memory usage — the file is never fully loaded
- • BOM and encoding detection: UTF-8/16, GB18030, Shift-JIS, EUC-KR, Windows-1252
- • Auto-detects comma, semicolon, tab and pipe delimiters
- • Long numeric IDs and leading-zero codes stay as text
- • RFC 4180 parser: quoted fields, commas and line breaks inside cells
- • Respects the Excel row limit (1,048,576 rows) with a clear truncation notice
- • 100% local — no upload, no signup
Frequently Asked Questions
Can this converter really handle a 100 MB CSV?
Yes. The converter reads your file as a stream of small chunks instead of loading it into memory, so files well above 100 MB convert without freezing or crashing the browser tab. The output XLSX is assembled locally while the data is parsed.
What is the file size limit?
Files up to 10 MB are free. Pro removes the size limit entirely — there is no server-side cap because all processing happens on your own device.
Will my CSV be uploaded to a server?
No. Everything runs locally in your browser with JavaScript. Your file never leaves your computer.
Why do my long numbers or ID columns display incorrectly in Excel?
Excel keeps only 15 significant digits for numbers, so long IDs such as order or phone numbers lose precision. This converter automatically keeps such columns — and codes with leading zeros — as text.
Related Tools
Need to edit the converted spreadsheet afterwards?
Open the online CSV editor