Convert CSV to Excel (XLSX)

Preserves leading zeros, long IDs, and dates that Excel would otherwise mangle. No upload, no install, no row cap.

When you'd convert CSV to Excel

Handing data to a non-technical recipient. Most business users live in Excel. Sending an XLSX is the lowest-friction way to share a dataset that someone else will open, filter, and chart.
Locking the schema. CSV columns are all strings on the wire. XLSX records per-column types, so when the recipient opens the file they get real numbers, real dates, and real text without rerunning type inference.
Avoiding Excel's auto-coercion. If you let Excel open a CSV directly, it will silently strip leading zeros from ZIP codes, convert long numeric IDs to scientific notation, and reformat dates by locale. Converting via ExploreMyData first preserves the original values.
Building reports. A CSV is data; an XLSX is a report. If the deliverable involves formatted numbers, frozen panes, or a column header row, XLSX is the right output.
Working offline later. Once you have the XLSX, you can open it in Excel, Numbers, Google Sheets, or LibreOffice without any internet connection.

Worked example: leading zeros that survive

Consider a CSV with US ZIP codes:

customer,zip,phone
Acme Corp,02139,5551234567
Beta Inc,90210,5559876543
Gamma LLC,07030,5552345678

If you double-click that CSV in Excel, ZIPs become 2139, 90210, 7030 (leading zero gone) and the phone column becomes 5.55E+09. ExploreMyData detects ZIP-like and long-numeric columns, marks them as text, and produces an XLSX where Excel leaves them alone:

customer    | zip    | phone
Acme Corp   | 02139  | 5551234567
Beta Inc    | 90210  | 5559876543
Gamma LLC   | 07030  | 5552345678

You can override the inferred type per column before export. If you wanted the phone column as a number for some reason, switch it back to integer in the schema panel.

Format-specific gotchas

Excel's row cap is 1,048,576 per sheet. If your CSV is larger, ExploreMyData warns you and offers to split across multiple sheets. The legacy XLS format is much smaller (65,536 rows) and we always default to XLSX.
Formula injection. A CSV value that starts with =, +, -, or @ would otherwise auto-execute as a formula when opened in Excel. We escape these to text by default. Worth knowing if you actually want a formula in the output.
Date locale ambiguity. "01/02/2026" is January 2 in the US and February 1 in most of the rest of the world. Unless the date is unambiguous (ISO 8601), we keep it as text rather than guess.
UTF-8 in cell values. XLSX is UTF-8 internally, so non-ASCII characters round-trip cleanly. The catch is the source CSV: if it's encoded as Latin-1 or Windows-1252 with a BOM mismatch, change the encoding in the CSV import dialog before exporting.
Sheet naming. Sheet names cap at 31 characters and disallow : \ / ? * [ ]. Long source filenames are truncated.
Cell type vs cell format. A cell type is what Excel will treat the value as in calculations; a cell format is just how it's displayed. We set both correctly for inferred types so downstream pivot tables and charts work without extra cleanup.

How this differs from the alternatives

vs Convertio, Zamzar, CloudConvert, FreeConvert. All four are server-side: the CSV gets uploaded to their data centre, converted, and downloaded. Free tiers have caps (Convertio 100 MB, Zamzar around 2 MB, CloudConvert metered minutes per day) and your data sits on their servers for up to 24 hours. ExploreMyData runs in your tab. No upload, no metering, no retention.
vs TableConvert. Browser-based, so privacy is comparable, but the free tier caps at 10 MB per file. ExploreMyData has no fixed cap.
vs opening the CSV directly in Excel. Excel costs money (Microsoft 365), and more importantly it auto-coerces values: leading zeros vanish, long numbers become scientific notation, dates get reformatted by locale. ExploreMyData preserves the raw values and writes them with explicit types.
vs Google Sheets (File > Import CSV > Download as XLSX). Free, but requires a Google account and uploads the file to Google Drive. Sheets applies its own date and number coercions during the import. ExploreMyData stays on-device with no account.
vs pandas (read_csv + to_excel). Works well, but you need Python plus openpyxl or xlsxwriter installed, and the API choices around per-column types are manual. ExploreMyData handles type inference and ZIP-style edge cases by default.

Frequently Asked Questions

What's the row limit when converting CSV to Excel?

Modern XLSX files cap at 1,048,576 rows per sheet. ExploreMyData warns you if your CSV exceeds that and offers to split across sheets, or to keep the data as CSV. The legacy XLS format is much smaller (65,536 rows), so we always default to XLSX.

Will leading zeros and long IDs be preserved?

Yes. ExploreMyData detects ID-like and ZIP-like columns and writes them as text in the XLSX so Excel doesn't strip leading zeros or convert long numeric strings to scientific notation. You can also force a column to text in the column profile before exporting.

How are dates handled?

If a CSV column parses unambiguously as a date (ISO 8601 like 2026-01-15), we write it as a real Excel date with a sensible default format. Ambiguous formats like "01/02/2026" are kept as text by default so we don't guess wrong; you can override the type if you know the format.

Are formulas like =SUM(...) executed or kept as text?

Cells starting with =, +, -, or @ are escaped to text by default. This prevents CSV-injection attacks where a malicious CSV would auto-execute a formula in Excel. If you actually want a formula, you can opt in per column.

Does the converter support multiple sheets?

A single CSV becomes a single sheet. If you want multiple sheets in the output, open multiple files in the workspace and export them together as a multi-sheet workbook. Sheet names default to the source filename.

Is there a file size limit?

No fixed limit beyond what your browser can hold in memory. DuckDB-WASM streams the CSV read, and the XLSX writer produces a compressed file. Hundreds-of-megabytes inputs work routinely.

Convert your CSV to Excel

No sign-up, no upload, no row cap. Leading zeros and long IDs survive.

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