How to open a large CSV file

Most tools try to load the whole file into memory at once, which is why a 1 GB CSV freezes Excel, Notepad and TextEdit alike. The fix is to stream the file — read it in chunks and never hold more than a fraction of it at a time. That is what this page does: drop a file and you get the row count, column names, detected delimiter and the first 20 rows, without loading the whole thing.

What works, and when

• Preview and count — this tool, or head -50 big.csv and wc -l big.csv in a terminal. Instant, regardless of size.
• Editing a few rows — a streaming-capable editor. VS Code handles a few hundred megabytes; Sublime Text and BBEdit go further. Notepad and TextEdit do not stream and will hang.
• Querying and aggregating — DuckDB is the best answer available: duckdb -c "select count(*) from 'big.csv'" runs over files far larger than memory. It needs an install and some SQL.
• Actually looking at all of it in a grid — you cannot, past about a million rows. Filter or split it down to something a spreadsheet can hold.

Check the encoding and delimiter before anything else

Two problems account for most "the file opened but it is garbage" reports. First, the delimiter may not be a comma — European exports frequently use semicolons, because the comma is the decimal separator. Second, the encoding may be UTF-16 or Windows-1252 rather than UTF-8, which turns accented characters into mojibake. Scanning a file here reports the detected delimiter, so you can confirm before importing it somewhere that will guess wrong silently.

A note on cloud converters

Uploading a large file to a free converter is slow, capped, and puts your data on a server you know nothing about. If the export contains customer records, that is a disclosure with legal weight in most of Europe. Local processing sidesteps the question entirely.

Related: CSV too large for Excel · Extract specific columns

Common questions

How do I count the rows in a huge CSV? Drop it here and read the row count, or run wc -l big.csv in a terminal. Both stream the file rather than loading it.

Why does my CSV open as one long column? The delimiter is not what your spreadsheet expected — usually a semicolon rather than a comma. Check the detected delimiter and set it explicitly on import.

Can I open a 5 GB CSV? You can scan, split and filter one here. You cannot view all of it in a spreadsheet; no spreadsheet holds that many rows.