CSV to XLSX Converter
Nothing leaves your browser — parsing, delimiter/encoding detection, and export all run locally.
Why this CSV to XLSX converter processes files in your browser
The top results for "csv to xlsx online" — CloudConvert, Convertio, FreeConvert — are general-purpose file-conversion platforms that happen to also handle spreadsheets, alongside video, PDF, and image formats. That breadth means your CSV gets uploaded to a shared conversion pipeline built for dozens of unrelated file types, with usage credits and accounts in the mix for anything beyond the free tier.
This tool does one thing: CSV to XLSX, entirely client-side. Parsing, delimiter detection, encoding fallback, and the .xlsx build all run in your browser's JavaScript engine. Nothing is uploaded, so there's no account, no credit limit, and no server log of what was in your file.
How it works
Drop one or more .csv files (or choose them). Each file's delimiter is auto-detected by checking which candidate — comma, semicolon, tab, or pipe — splits every sampled line into the same number of fields; this matters because European exports frequently use semicolons (since commas are the decimal separator) and tab-separated exports are common from database tools.
Character encoding is handled the same way: the file is first decoded as UTF-8, and if that fails validation (a tell-tale sign of an older Windows/Excel export saved as Latin-1 / Windows-1252), it's automatically re-decoded as Latin-1 instead of silently mangling accented characters into garbled text.
Once parsed, column types (numbers, ISO dates, booleans) are inferred and applied as real Excel number formats, and each CSV becomes its own sheet in a single downloaded workbook — or, if you turn on "one .xlsx per CSV file," each file downloads as its own separate workbook instead, matching how it started.
What's included
Multi-file batch conversion in one pass — drop 5 CSV exports and get one workbook with 5 sheets (or 5 separate .xlsx files), rather than converting one at a time like most of the free single-file tools we checked. A live preview table per file before you export, with per-file row and column counts and the detected delimiter shown so you can catch a misdetected file early.
A frozen header row and auto-filter dropdowns on by default, matching the other converters on this site, so the resulting workbook is immediately usable — sortable, filterable — rather than needing manual formatting after the fact.
Limitations, and when to reach for something else
Delimiter detection looks at the first 10 non-empty lines; a file with wildly inconsistent formatting in its early rows (mixed delimiters, a free-text preamble before the real header) can occasionally need a manual fix in a text editor first. Encoding detection covers the two most common cases (UTF-8 and Latin-1/Windows-1252) — a file saved in a less common legacy encoding may still show garbled characters.
If your source is already an .xlsx or you need to read Excel back into JSON, use the Excel to JSON converter linked below. If you're merging several CSV or Excel files into one combined table rather than converting formats, Merge Excel Files is the more direct tool for that job.
Need a spreadsheet built to run your business, not just hold data?
These converters get your data into a spreadsheet. Our templates go further — dashboards, automations, and data validation built in, tested to the cent, in matching Excel and Google Sheets versions.
Frequently asked questions
Is my CSV file uploaded anywhere?
No. Parsing, delimiter/encoding detection, and the .xlsx export all run in your browser using JavaScript — nothing is sent to a server. You can disconnect from the internet after the page loads and the tool still works.
How does the delimiter auto-detection work?
The tool checks the first several lines of your file against comma, semicolon, tab, and pipe, and picks whichever one splits every line into the same number of fields — the signature of a real delimiter versus a comma that just happens to appear inside a value.
My CSV has accented characters that look broken — what happened?
That's usually a Latin-1 (Windows-1252) file, common from older Excel exports on Windows. This tool detects that automatically: it tries UTF-8 first, and falls back to Latin-1 if the bytes aren't valid UTF-8, so accented characters decode correctly either way.
Can I convert several CSV files at once?
Yes. Drop multiple files and choose whether you want one workbook with a sheet per file, or a separate .xlsx download for each CSV — both options are available.
What's the largest file this can handle?
Roughly 50MB per file comfortably. Parsing and export run in your browser's JavaScript thread, so a very large file can cause a brief pause while it's processed rather than a crash.