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CSV to Excel (XLSX) Converter

Turn CSV files into Excel documents in a couple of clicks — the file you get is a .xlsx, which is what Excel saves and opens. Flat tabular text — one table, no formatting. Content is preserved and the layout is rebuilt for the target format.

Not uploaded to any serverConverted on this deviceGone when you close the tabHow this works

Drop your files here

CSV files (.csv) · up to 100 MB each

or paste files from your clipboard

Ready when you are

Drop a CSV file above and FileTools360 will turn it into XLSX — right here on your device, without uploading anything.

⌘K to search converters

How to use it

  1. 1

    Add your CSV files

    Drag them onto the drop area, choose them from your device, or paste them from your clipboard. You can queue several at once. Nothing is sent anywhere — the file stays on this device.

  2. 2

    Adjust the settings if you want to

    The defaults suit most people. Open Advanced to control delimiter and header handling.

  3. 3

    Convert and download

    Press Convert. Everything happens on your own device — nothing is uploaded. Download files one by one, or grab them all as a ZIP.

Privacy, in plain words

Is it safe? Your CSV file is not uploaded anywhere

What “uploaded” normally means. On most online converters, pressing the button copies your file across the internet onto a computer owned by that website. That copy is what the word “upload” means, and it is the part nobody explains.

What happens instead. This site does not do it. There is no server here that receives files, so your CSV file is read, converted and handed back by the browser you are using right now. It never travels — so there is no copy to store, read, leak or hand over.

Check it yourself in ten seconds

Turn off your Wi-Fi after this page has loaded, then convert a file anyway. It still works, because everything needed is already on your device.

The longer explanation of how this works, and the full detail of what is and is not stored on the privacy page.

Why this matters more than it sounds

A spreadsheet is rarely about one person. It is usually about hundreds of them, which is what turns an ordinary file into a reportable data breach. It matters more than it sounds, because of what spreadsheets usually are:

Customer and member lists

names, emails, phone numbers, addresses

Patient or client records

regulated personal data under HIPAA, GDPR and similar

Financial models and forecasts

numbers a competitor would pay for

Supplier pricing

commercially confidential by contract, usually

A file that is never sent cannot be kept, leaked, subpoenaed or used to train anything. That is a property of how this works, not a promise about how carefully it is run.

CSV and XLSX explained

CSV is plain text where each line is a row and commas separate the fields. There is no formatting, no formulas, and no second sheet — which is precisely why every system on earth can read it.

XLSX is Excel's modern format — a ZIP of XML holding cells, formulas, formatting, multiple sheets, charts and pivot tables.

Where CSV files come from
Database exports, analytics tools and data interchange between systems.
Where XLSX is used
Excel, Google Sheets exports and business reporting systems.

CSV vs XLSX

The two formats solve different problems, which is why converting between them involves trade-offs rather than a straight upgrade.

CSV compared with XLSX
PropertySourceTarget
CompressionNoneLossless
Introduced—2007
Browser supportEvery spreadsheet, database and programming language.Excel, Google Sheets, Numbers, LibreOffice.
CSV is stronger at
Readable by every spreadsheet, database and programming language. Plain text, so it diffs and streams well. Tiny files.
XLSX is stronger at
Formulas, formatting, charts and multiple sheets in one file. Compact relative to the old .xls. Supported by Excel, Sheets, Numbers and LibreOffice.

Why convert CSV to XLSX?

People make this switch when they run into the limits of CSV: the data needs formulas, formatting or multiple sheets. XLSX is the better fit when the data needs calculation, formatting or more than one sheet.

CSV limitations that prompt the switch
Exactly one table — no sheets, formatting or formulas. No type information, so leading zeros and long numbers get mangled. The 'comma' is not guaranteed; European exports often use semicolons.
What you give up
Harder to parse programmatically than CSV. Formula compatibility varies between applications.

What is preserved when converting CSV to XLSX?

The content survives; the layout is rebuilt. Text and the order it is read in carry across, but XLSX lays the page out again rather than reproducing CSV's exact positioning, so line breaks, page breaks and spacing will differ. Anything that depends on precise placement is worth checking in the result.

CSV has no notion of data types. A product code like 007 becomes 7 unless the importing tool is told otherwise — which is a property of CSV, not a bug in the converter.

Measured, not estimated

What converting CSV to XLSX actually costs

On every sample measured, the XLSX came out larger — 16× larger at best and 57× larger at worst.

Each row is one sample chosen to isolate a property these formats treat differently.
SampleCSV inXLSX outChange
A plain tableTen rows of flat records — the shape almost every spreadsheet export actually has.380 B17.5 KB47×
Many columnsForty columns across three rows. Column-heavy data is where per-cell overhead shows up.1.3 KB20.3 KB16×
Nested recordsObjects inside objects. This is the shape that cannot survive a flat format intact, and the one that triggers a warning.301 B16.8 KB57×
Commas and quotation marksText fields containing the delimiter and the quote character — where an escaping bug would show.875 B17.2 KB20×

Produced by this site's own converter. The same code that runs in your browser, at the same default settings, so these are the bytes you would download.

Samples are generated from a fixed seed rather than taken from real photographs or documents, so the corpus is reproducible and carries no licensing question — and so the numbers predict the shape of your result rather than its exact size. Measured 2026-10-01. The method, and the command that regenerates every figure on this page, are on the how it works page.

About these formats

Source

Comma-Separated Values

Flat tabular text — one table, no formatting.

Extensions
.csv
MIME type
text/csv
Best for
Data imports and exports · Databases · Scripts
Compatibility
Every spreadsheet, database and programming language.

Target

Excel Open XML Workbook

The modern Microsoft Excel workbook format.

Extensions
.xlsx, .xlsm
MIME type
application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
Best for
Multi-sheet data · Formulas · Business reporting
Compatibility
Excel, Google Sheets, Numbers, LibreOffice.

Values are type-sniffed, so numbers and dates land as real numbers and dates rather than text.

Good to know

CSV to Excel (XLSX) Converter — questions

How do I convert CSV to XLSX?

Drop your CSV file onto the area above, then press Convert. The XLSX file saves straight to your device. You do not need an account, and there is no watermark.

Is it safe to convert CSV files here — are they uploaded to a server?

No, nothing is uploaded. On most online converters, pressing the button copies your file across the internet onto a computer owned by that website; it is converted there and sent back. That copy is what "upload" means, and it is the part that puts your file out of your control. This site does not do it. Your CSV file is read and converted by the browser you are using right now and never leaves this device, so there is no copy for anyone to store, read or hand over. You can prove it: turn off your Wi-Fi after this page loads and the conversion still works.

Can I convert confidential CSV files, like bank statements or contracts?

Yes, and that is the case this site was built for. Because the file never leaves your device, a confidential document is no more exposed than it is sitting in your own folder — there is no transfer, no copy on someone else's hardware, no retention period to read about and no staff with access. Nothing is logged about the file either: not its name, not its size, not its contents. The one thing worth saying plainly is that this protects the file in transit and at rest on our side, not from anything already on your own computer.

What should I know before converting CSV to XLSX?

Values are type-sniffed, so numbers and dates land as real numbers and dates rather than text.

What is preserved when converting to XLSX?

Text, structure and images carry over faithfully. Exact page layout does not, because XLSX lays content out differently from CSV. Check headings, tables and page breaks in the result.

How large a file can I convert?

Up to 100 MB per file for this conversion. Because the work happens in your browser, the practical limit is your device's memory — larger files work on a desktop with plenty of RAM and may fail on an older phone.

Can I convert several files at once?

Yes. Add as many as you like and press Convert All. Each file is processed independently, so one failure does not stop the rest, and you can download everything together as a ZIP.

Can I use this on my phone?

Yes. FileTools360 works in mobile browsers on iOS and Android. Pick the file through your phone's file picker — Files on iOS, or Downloads on Android — including files stored in iCloud or Google Drive.

Read more about these formats

CSV vs XLSX: Which Should You Use for Your Data?

Why your product codes lose their leading zeros, and which format to blame.

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FileTools360 by the numbers

527 converters and tools65 file formatsnothing ever uploaded.