File Compression in C# with System.IO.Compression

File Compression in C# with System.IO.Compression


In software development, managing file sizes efficiently is crucial. Whether it’s for saving disk space, optimizing data transfer, or archiving purposes, file compression plays a pivotal role. In the .NET framework, the System.IO.Compression namespace provides a powerful yet straightforward way to handle file compression and decompression in C#.

This blog post will guide you through using this library effectively in your C# applications.

Understanding System.IO.Compression

The System.IO.Compression namespace contains classes that provide basic compression and decompression services for streams. The primary classes include ZipArchive for handling ZIP files and GZipStream and DeflateStream for compressing and decompressing data using the Gzip and Deflate compression algorithms, respectively.

Getting Started

To use the System.IO.Compression library, ensure your C# project references the System.IO.Compression and System.IO.Compression.FileSystem assemblies. These are usually included by default in recent .NET versions.

Using ZipArchive for ZIP Operations

Creating a ZIP File

using (var zip = ZipFile.Open("", ZipArchiveMode.Create)) 
    zip.CreateEntryFromFile("file.txt", "file_in_zip.txt"); 

This code snippet creates a ZIP file named and adds file.txt from the disk, renaming it to file_in_zip.txt within the ZIP.

Extracting a ZIP File

ZipFile.ExtractToDirectory("", "extracted_folder");

This extracts the contents of into a folder named ‘extracted_folder‘.

Working with GZipStream and DeflateStream

Compressing Data

using (var originalFileStream = new FileStream("file.txt", FileMode.Open)) 
using (var compressedFileStream = File.Create("file.gz")) 
using (var compressor = new GZipStream(compressedFileStream, CompressionMode.Compress)) 

This compresses file.txt into a Gzip file file.gz.

Decompressing Data

using (var compressedFileStream = new FileStream("file.gz", FileMode.Open)) 
using (var decompressedFileStream = File.Create("file_decompressed.txt")) 
using (var decompressor = new GZipStream(compressedFileStream, CompressionMode.Decompress)) 

This decompresses file.gz back into a text file.

Best Practices and Tips

  • Error Handling: Always implement proper error handling, especially when dealing with file I/O operations.
  • Using Statements: Utilize using statements for stream operations to ensure proper disposal of resources.
  • File Paths: Be cautious with file paths and names to avoid overwriting existing files unintentionally.
  • Performance Considerations: Compression can be CPU-intensive. For large files or high-volume scenarios, consider performance impacts.

Advanced Scenarios

  • Memory Streams: You can compress/decompress data in memory using MemoryStream instead of file streams.
  • Custom Compression Levels: Adjust the compression level for a balance between speed and compression ratio.
  • Working with Bytes: You can directly work with byte arrays for compression and decompression, useful for network operations or binary data processing.


The System.IO.Compression namespace in C# offers a powerful and easy-to-use set of tools for handling file compression, making it an essential skill for developers working with file systems or data transfer.

By understanding and leveraging these classes, you can efficiently manage file sizes and optimize storage and data transmission in your .NET applications.


Hi, my name is Stephen Finchett. I have been a software engineer for over 30 years and worked on complex, business critical, multi-user systems for all of my career. For the last 15 years, I have been concentrating on web based solutions using the Microsoft Stack including ASP.Net, C#, TypeScript, SQL Server and running everything at scale within Kubernetes.