LZMA Compress & Decompress
Compress and decompress LZMA (.lzma) files entirely in your browser. Adjustable compression levels 1-9, real-time progress tracking, and instant decompression with no server uploads.
How to Use
Compress any file into LZMA format or decompress existing .lzma files, entirely within your browser. No uploads, no installations, no file size limits beyond your browser's memory.
Compressing a File
- Select Compress mode using the segmented control at the top. This is the default mode when the tool loads.
- Choose a compression level using the slider. Level 1 is the fastest with moderate compression; level 5 offers a balanced tradeoff; level 9 produces the smallest output but takes the longest. The default is level 5.
- Drop or select your file. Any file type is accepted — text files, JSON, executables, archives, images, or any other format.
- Wait for processing. A progress bar shows real-time compression progress. LZMA compression is more CPU-intensive than GZIP, so larger files at higher levels may take several seconds.
- Review results. The tool displays the original size, compressed size, compression ratio as a percentage, and total processing time.
- Download the compressed file. Click the download button to save the
.lzmafile. The output filename is your original filename with.lzmaappended.
Decompressing a File
- Select Decompress mode using the segmented control — or simply drop an
.lzmafile while in Compress mode. The tool auto-detects LZMA format by inspecting the header bytes and switches to Decompress automatically. - Drop or select the LZMA file. While
.lzmais the standard extension, the tool validates by header structure rather than file extension. - Review results. The tool displays the compressed size, decompressed size, compression ratio, and processing time.
- Download the decompressed file. The output filename defaults to the original name with the
.lzmaextension stripped. If the input filename does not end in.lzma, a.decompressedsuffix is added.
About This Tool
The LZMA Algorithm
LZMA (Lempel-Ziv-Markov chain Algorithm) was developed by Igor Pavlov for the 7-Zip archiver in 1998. It combines three compression techniques: LZ77 dictionary compression with a sliding window up to 4 GB, range encoding (an arithmetic coder that is more efficient than Huffman coding), and Markov chain context modeling that predicts the next byte based on the current state. This layered approach produces compression ratios that consistently beat GZIP by 20-50% on most data types.
LZMA vs DEFLATE (GZIP)
GZIP uses the DEFLATE algorithm, which combines LZ77 with Huffman coding and a maximum 32 KB sliding window. LZMA uses a much larger dictionary (up to 4 GB vs 32 KB), range encoding instead of Huffman coding, and sophisticated context modeling. The larger dictionary means LZMA can find repeated patterns separated by megabytes of data, which DEFLATE cannot. The tradeoff is that LZMA compression is significantly slower — typically 5-10x slower than GZIP at equivalent quality. However, LZMA decompression is fast (often faster than GZIP decompression) because the decoder is simpler than the encoder.
LZMA File Format
The raw LZMA format consists of a 13-byte header followed by the compressed data stream. The header contains: a properties byte encoding the literal context bits (lc), literal position bits (lp), and position bits (pb); a 4-byte dictionary size in little-endian format; and an 8-byte uncompressed size (set to all 0xFF bytes when the size is unknown). Unlike GZIP, raw LZMA does not store the original filename, timestamps, or checksums — these features are provided by container formats like .7z or .xz.
Compression Levels Explained
LZMA compression levels control two primary parameters: dictionary size and match finder cycles. Level 1 uses a 64 KB dictionary with fast hash-chain matching, suitable for real-time compression of smaller files. Level 5 uses a 4 MB dictionary with binary-tree matching, offering the best balance between speed and compression for most workloads. Level 9 uses a 32 MB dictionary with exhaustive matching, requiring up to 10x the memory of level 1 but achieving the best possible compression ratio. For text-heavy files like source code, log files, or JSON documents, the difference between level 5 and level 9 is typically 2-5% better compression at the cost of 3-8x more processing time.
Why Use This Tool
When to Use LZMA Compression
LZMA is ideal when file size matters more than compression speed. Here are the most common use cases:
- Software distribution — Installers and update packages use LZMA to minimize download sizes. The NSIS installer, Inno Setup, and Android APK expansion files all use LZMA internally. A 100 MB application that compresses to 40 MB with GZIP might reach 25 MB with LZMA.
- Archival storage — When files are compressed once and stored for long periods, the extra compression time is negligible compared to ongoing storage costs. Database backups, audit logs, and compliance archives benefit from LZMA's superior ratios.
- Embedded systems — Linux kernel images and initramfs archives use LZMA (via
lzmaorxz) because flash storage is expensive and decompression is fast even on low-power CPUs. - Game asset packaging — Game developers use LZMA to compress textures, models, and audio assets. The fast decompression speed means assets load quickly at runtime despite being heavily compressed on disk.
- Log file compression — Server log files are highly repetitive and compress exceptionally well with LZMA. A 1 GB log file that GZIP compresses to 100 MB might reach 30-50 MB with LZMA at level 9.
LZMA vs Other Compression Formats
- vs GZIP — LZMA achieves 20-50% better ratios but is 5-10x slower to compress. Use GZIP for HTTP content encoding and real-time compression; use LZMA for archival and distribution.
- vs Brotli — Brotli (used in HTTP compression) achieves ratios between GZIP and LZMA with faster decompression. LZMA still wins for offline compression of non-web content.
- vs Zstandard (zstd) — Zstandard offers LZMA-level ratios at near-GZIP speeds. It is the modern choice for real-time compression. LZMA remains the standard for 7-Zip archives and legacy compatibility.
Privacy
Your files never leave your browser. The LZMA algorithm runs entirely in JavaScript within your browser tab — no data is sent to any server, no temporary files are created on remote infrastructure, and no third-party services are contacted. This makes the tool safe for compressing sensitive documents, configuration files with credentials, proprietary source code, or any data that must remain private.
Related Tools
Explore other file tools on DevToolkit: GZIP Compress & Decompress for faster compression with native browser APIs, Hex Dump Viewer for inspecting binary file contents, Reverse File for byte and line reversal, Random Binary Generator for creating test files, and File Checksum for verifying file integrity with SHA-256 hashes.