Extremely Fast Compression algorithm
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LZ4 - Extremely fast compression

LZ4 is lossless compression algorithm, providing compression speed at 400 MB/s per core, scalable with multi-cores CPU. It features an extremely fast decoder, with speed in multiple GB/s per core, typically reaching RAM speed limits on multi-core systems.

Speed can be tuned dynamically, selecting an "acceleration" factor which trades compression ratio for more speed up. On the other end, a high compression derivative, LZ4_HC, is also provided, trading CPU time for improved compression ratio. All versions feature the same decompression speed.

LZ4 library is provided as open-source software using BSD 2-Clause license.

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Branch Policy:

  • The "master" branch is considered stable, at all times.
  • The "dev" branch is the one where all contributions must be merged before being promoted to master.
    • If you plan to propose a patch, please commit into the "dev" branch, or its own feature branch. Direct commit to "master" are not permitted.


The benchmark uses lzbench, from @inikep compiled with GCC v6.2.0 on Linux 64-bits. The reference system uses a Core i7-3930K CPU @ 4.5GHz. Benchmark evaluates the compression of reference Silesia Corpus in single-thread mode.

Compressor Ratio Compression Decompression
memcpy 1.000 7300 MB/s 7300 MB/s
LZ4 fast 8 (v1.7.3) 1.799 911 MB/s 3360 MB/s
LZ4 default (v1.7.3) 2.101 625 MB/s 3220 MB/s
LZO 2.09 2.108 620 MB/s 845 MB/s
QuickLZ 1.5.0 2.238 510 MB/s 600 MB/s
Snappy 1.1.3 2.091 450 MB/s 1550 MB/s
LZF v3.6 2.073 365 MB/s 820 MB/s
Zstandard 1.1.1 -1 2.876 330 MB/s 930 MB/s
Zstandard 1.1.1 -3 3.164 200 MB/s 810 MB/s
zlib deflate 1.2.8 -1 2.730 100 MB/s 370 MB/s
LZ4 HC -9 (v1.7.3) 2.720 34 MB/s 3240 MB/s
zlib deflate 1.2.8 -6 3.099 33 MB/s 390 MB/s

LZ4 is also compatible and well optimized for x32 mode, for which it provides +10% speed performance.


The raw LZ4 block compression format is detailed within lz4_Block_format.

To compress an arbitrarily long file or data stream, multiple blocks are required. Organizing these blocks and providing a common header format to handle their content is the purpose of the Frame format, defined into lz4_Frame_format. Interoperable versions of LZ4 must respect this frame format.

Other source versions

Beyond the C reference source, many contributors have created versions of lz4 in multiple languages (Java, C#, Python, Perl, Ruby, etc.). A list of known source ports is maintained on the LZ4 Homepage.