What Is Parquet? The Columnar File Format Explained

Parquet is the file format most data tools prefer. Here is what it is and why.

Parquet is an open file format for tables. Instead of writing one row after another, as CSV does, it stores all the values of one column together. This is called a columnar format. It is used by tools such as Apache Spark, DuckDB, BigQuery, Snowflake and pandas.

Storing columns together has two big advantages. First, values in one column are similar, such as a list of cities, so they compress very well and files are small. In our test, a 6.87 MB CSV became a 1.84 MB Parquet file. Second, a query that needs only two columns can read just those two columns from disk, instead of every row in full.

Parquet also keeps a type for each column, such as integer, decimal, text or date, and information about the data inside each block, so tools can skip blocks that cannot match a filter. A CSV has no types at all, which is why a number can turn into text or a leading zero can disappear when a CSV is opened.

The trade-off is that Parquet is not human readable. You cannot open it in a text editor or in most spreadsheets. To look inside, use a tool that reads Parquet, such as the free Data Utility converter, which shows the table and converts it to CSV, JSON or Excel in your browser. Use CSV when people need to read or edit the file, and Parquet when machines will process it.

Open the Parquet to CSV 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.
  • CSV to Parquet Converter: Convert CSV 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.
  • 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 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 Parquet to CSV converter: step by step

  1. Open the Parquet to CSV converter.
  2. Drop in your Parquet file.
  3. Check the columns and types in the preview.
  4. Download it as CSV, JSON or Excel if you need it.

When to use the Parquet to CSV converter

  • Understand why a data team asks for Parquet
  • Choose a format for a data lake
  • Open a Parquet file you received
  • Explain Parquet to a non-technical colleague

Example

Input: A Parquet file with the columns id, name and age.

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

Frequently asked questions

How do I convert Parquet to CSV?

Drop your Parquet file (or paste the data), check the options, click Convert and download the CSV 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: If a Parquet file will not open in Excel, convert it to CSV or Excel first.