Convert CSV to Excel without breaking leading zeros, IDs, or dates. Control column types to preserve data integrity.
Note: All processing happens locally in your browser. No files are uploaded.
CSV is the default export format for almost everything. Every database, reporting tool, and API dump can spit one out. The trouble starts the moment someone opens that CSV in Excel: leading zeros disappear, long IDs flip to scientific notation, dates get reinterpreted by locale, and UTF-8 characters turn into mojibake. By converting CSV to XLSX up front with explicit column types, you lock the data down before Excel ever touches it.
The converter runs entirely in your browser, so nothing uploads and your data never leaves your machine. It handles CSVs up to a few hundred megabytes, and the XLSX output opens cleanly in Excel, Numbers, Google Sheets, LibreOffice, and anything else that reads the format.
Opening a CSV directly in Excel is a coin flip. These are the specific things that break, and what the converter does about each one.
Excel will happily turn 01234 into 1234 and 012345678901 into the number 12,345,678,901, dropping the leading zeros on the way. This tool writes affected columns as text, so the zeros stay put.
Any numeric value with more than 15 digits loses precision in Excel. Credit card numbers, tracking numbers, and bigint primary keys all end up rendered as something like 1.23457E+16. The converter detects wide numbers and writes them as text so the full digits stay intact.
03/04/2024 is March 4th in the US and April 3rd in the UK. Excel picks one based on your locale and you may not notice until a client complains. Date parsing here is opt-in. Leave it off and dates round-trip as plain text, exactly as they appeared in the CSV.
CSVs with accented characters, Asian scripts, or emoji often come out as question marks or garbled bytes when Excel reads them. This tool writes XLSX directly, bypassing Excel's quirky CSV import path entirely, so characters survive the round trip.
European CSVs often use semicolons. Tab-separated files use tabs. The tool auto-detects the delimiter, but you can force one manually if auto-detection guesses wrong.
CSV (Comma-Separated Values) is a plain-text format. It's human-readable, universally supported, and tiny, but it has no concept of column types, cell formatting, multiple sheets, or formulas. XLSX (Excel's modern format, officially Office Open XML Spreadsheet) is a zipped XML bundle that stores types, styles, sheets, and formulas.
Use CSV when you're moving data between systems that don't care about presentation, like database dumps, script pipelines, or loading into another tool. Use XLSX when a human will open the file in Excel, when columns must retain their type, or when the same file has to serve as both storage and a viewable report.
With this converter in the loop, your source data can stay as a clean, portable CSV, and you only generate a typed XLSX when you need to hand the data to someone.
Yes. Completely free, no signup, no ads, no usage limits. The tool runs entirely in your browser, so there are no server costs to cover.
No. The conversion happens entirely in your browser using client-side JavaScript. Your CSV never leaves your device, which matters if it contains customer data, financial records, or anything else you'd rather not send to a third party.
Several hundred megabytes in modern browsers. Very large files can take a few seconds to process. The browser tab's memory limit is the only real bottleneck; there is no arbitrary cap from us.
Yes. By default, auto-detect marks any column where values start with 0 as text, so 01234 stays 01234. You can also tick "Treat ALL columns as text" for the most defensive setting.
Yes. The delimiter is auto-detected by default. If auto-detection picks wrong (rare, but it happens with mixed content), type the delimiter into the Delimiter field: ; for semicolons, \t for tabs, or | for pipes.
XLS is the legacy binary format from Excel 97-2003. XLSX (the "X" stands for XML) is the modern ZIP-based Office Open XML format introduced in Excel 2007. XLSX files are smaller, recover better from corruption, and are supported by every spreadsheet program made in the last 15+ years. This tool outputs XLSX only.