Convert CSV to Parquet: pandas, DuckDB or Your Browser

There are three common ways to turn a CSV into Parquet. Here is how each works and when to use it.

Option 1: pandas. If you already use Python, read the file with pandas.read_csv and write it with DataFrame.to_parquet. You need the pyarrow or fastparquet package installed. This gives you full control over column types and compression, and it fits into a script. The downside is that the whole file is loaded into memory, so very large files can be slow, and everyone who runs the script needs a Python setup.

Option 2: DuckDB. DuckDB can read a CSV and write Parquet with one SQL command: COPY (SELECT * FROM read_csv_auto('data.csv')) TO 'data.parquet' (FORMAT PARQUET). It streams the file, so it handles files larger than memory and is very fast. It needs the DuckDB program or library installed and some comfort with SQL.

Option 3: your browser. With the free Data Utility converter you drop the CSV on the page and download the Parquet file. There is nothing to install, no account and no upload, because the conversion runs on your device. In our test, 100,000 rows converted in under half a second. It suits one-off conversions, quick checks, and people who do not use Python or SQL. For files over about 100 MB, a desktop tool such as DuckDB is a better fit.

How to choose. For a repeatable data pipeline, use pandas or DuckDB inside your script. For a single file, or when you cannot install software, use the browser tool. Whichever you choose, check the result by opening the Parquet file again and comparing the row count and the column types.

Open the CSV to Parquet converter

Related tool pages

  • JSON, CSV, Parquet and Excel Converter: Convert between JSON, CSV, Parquet and Excel online for free, one file or a whole folder. It runs in your browser, so nothing is uploaded.
  • JSON to CSV Converter: Convert JSON to CSV online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • CSV to JSON Converter: Convert CSV to JSON online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • JSON to Parquet Converter: Convert JSON to Parquet online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • Parquet to CSV Converter: Convert Parquet to CSV online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.
  • Parquet to JSON Converter: Convert Parquet to JSON online for free. Drop a file or paste data, click convert and download. It runs in your browser, so your data is never uploaded.

How to use the CSV to Parquet converter: step by step

  1. Decide how big the file is and how often you convert.
  2. For one file, open the browser converter and drop the CSV in.
  3. For a pipeline, use pandas or DuckDB in your script.
  4. Open the result and check the rows and types.

When to use the CSV to Parquet converter

  • Convert a one-off export without installing anything
  • Pick the right method for a data pipeline
  • Handle a CSV that is too large for pandas
  • Check a converted file

Example

Input: id,name,age 1,Ada,36 2,Alan,41

Output: A Parquet file with the same columns (id, name, age) and typed values.

Frequently asked questions

How do I convert CSV to Parquet?

Drop your CSV file (or paste the data), check the options, click Convert and download the Parquet result.

How big can a file be?

It depends on your device. A few hundred MB usually works.

Which conversions does the Format Converter support?

Any direction between JSON, CSV, Parquet and Excel (.xlsx), for one file or a whole folder. Nested JSON is flattened into columns such as address.city. For Excel, the first sheet is read; old .xls files are not supported.

Why did my number or date change after converting?

Types are detected from the values. Turn off "Detect types" to keep everything as text, which also keeps leading zeros in IDs and phone numbers.

Tip: After converting, open the Parquet file in the Data Profiler to check the row count and column types.