BZ3 File

What are BZ3 files and how to open them

Are you having problems opening a BZ3 file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BZ3 files.

What is a BZ3 file?

A .BZ3 file is a BZip3 Compressed Archive file.

BZip3 compressed archive files are losslessly compressed data streams produced by the tool "bzip3," which is designed as a modern replacement for bzip2. They're used to reduce file size for single files or data streams by applying a sequence of compression stages including run-length encoding (RLE), Lempel-Ziv Prediction (LZP), the Burrows-Wheeler transform (via suffix-array implementation), and an order-0 arithmetic coder. These files are typically created when someone runs bzip3 to compress data, or by code using the libbz3 library's high-level API functions. Decompression restores the original content exactly.

The format supports block-based compression, where data is divided into blocks of configurable size (minimum 1 MiB, up to 511 MiB), with a default block size of 16 MiB. Smaller data (< 64 bytes) may be stored without compression. A CRC32 is computed on uncompressed data before compression and checked after decompression to detect corruption. Multi-threaded encoding or decoding is supported via parallel block processing.

Files start with a fixed header identifying the format. A signature "BZ3v1" in ASCII (bytes 0x42 5A 33 76 31) appears at offset 0, which distinguishes this format from other archive types.

How to open BZ3 files

Important: Different programs may use files with the BZ3 file extension for different purposes, so unless you are sure which format your BZ3 file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 25, 2026

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