Convert LZ to 7Z Online (Two Formats That Actually Share the Same Compression Algorithm)

Two Archive Formats Built Around the Same Compression Core

Lzip is a compression format created by Antonio Diaz Diaz and first released in 2008, documented in a published IETF Internet-Draft that also registers "application/lzip" as a formal media type. The 7z format was developed by Igor Pavlov and first released the same year as the original 7-Zip program, 1999, nearly a decade earlier than lzip. Despite that gap, both formats compress data using LZMA at their core — 7z later added LZMA2, Pavlov's own refinement of the same algorithm, as its default method starting with 7-Zip 9.20, but the underlying dictionary-matching approach both formats rely on traces back to the same LZMA design.

Where the two formats genuinely diverge is in what wraps around that shared compression core. A .lz file opens with a fixed four-byte signature — 0x4C 0x5A 0x49 0x50, "LZIP" in ASCII — followed by a version byte, a coded dictionary-size byte, the LZMA-compressed data, and a trailer holding a CRC32, the original data size, and the compressed member size, which lzip's own documentation calls a "3-factor integrity check." A .7z file is structured entirely differently: it uses a signature header followed by a separate, flexible "header" section describing however many internal streams the archive contains, each protected by its own CRC32, with the file layout itself documented in the 7z format specification distributed alongside the 7-Zip and p7zip source code.

Why This Conversion Rarely Changes Compression Ratio Much

Because both formats already run the same core LZMA algorithm, converting a .lz file to .7z is fundamentally different from converting, say, a gzip-based format to something LZMA-based — there's no jump from a small DEFLATE window to a much larger LZMA one, since lzip already used LZMA to begin with. The size difference that does show up between the two, when there is one, usually comes from container overhead and from 7z's support for "solid" archiving, where multiple files of similar type get compressed together as one combined stream to exploit redundancy between them, something a single lzip-compressed file, which only ever holds one continuous stream by design, has no equivalent concept of.

That single-stream design is also why converting a multi-file .tar.lz archive into .7z genuinely changes the internal structure, not just the wrapper. A .tar.lz file's contents remain accessible only by decompressing the entire lzip stream and then reading through tar's sequential 512-byte headers to find any one file. A .7z archive, once built with multiple internal streams rather than one combined tar layer, can expose files with their own individually addressable entries in the archive's header section — a structural difference that has nothing to do with which compression algorithm either format happens to use underneath.

What Moving From LZ to 7z Actually Changes

• Gain — far broader native software support: 7z is 7-Zip's own default format and opens directly in the free 7-Zip program on Windows, while .lz generally needs the separate Lzip7z plugin or a dedicated package.
• Lose — lzip's three-factor integrity check: 7z protects its internal streams with per-stream CRC32 values, a different, less unified approach than lzip's combined data-size-plus-member-size trailer.
• Gain — real, documented encryption: 7z supports AES-256 encryption including optional header encryption, which hides even the archive's file listing; lzip's format has no encryption mechanism built in at all.
• Gain — native multi-file structure: 7z handles multiple files directly, without needing a separate tar step the way a plain .lz archive does for anything beyond a single stream.
• Lose — lzip's documented recovery tooling: lziprecover is built specifically around lzip's own trailer format; 7z has no bundled equivalent tool tied that directly to its own header structure.
• Roughly unchanged — raw compression ratio on a single file: since both formats already use LZMA-family compression, converting between them changes container overhead more than it changes how tightly the actual data packs.

Where 7z Already Works and Where LZ Still Needs Extra Setup

7z is the default, native format of 7-Zip itself, a free program available on Windows, and p7zip brings the same format to Linux and macOS. Beyond that, Windows 11 began integrating the open-source libarchive project directly into File Explorer, with Microsoft rolling out native read support for 7z, RAR, TAR, and GZ archives in 2023, followed by native write support for 7z and TAR specifically in the Windows 11 24H2 update — meaning a modern Windows 11 system can now open and even create some 7z archives with zero extra software installed, though the built-in experience does not support password-protected archives.

Lzip's support picture is narrower by comparison. GNU tar has handled it transparently since version 1.23 through its own --lzip option, and GNOME's Archive Manager opens the format directly on Linux, but 7-Zip's own standard build does not include native lzip support — it requires the separate Lzip7z plugin — and WinRAR's documented list of formats doesn't include lzip at all. Real adopters of the .lz format include the IANA Time Zone Database and the Linux-libre kernel project, both of which ship some releases this way, but that's still a narrower footprint than 7z's, which sits as 7-Zip's own default output format.

macOS shows a similar gap on the lzip side: there's no documented native lzip support in Finder or Archive Utility, and Homebrew's lzip package is the practical route to opening one there, while the free Keka app and p7zip both handle 7z directly without any extra plugin hunting. That asymmetry — 7z already sitting inside the default toolchain on more systems, .lz needing something extra almost everywhere outside Linux — is a large part of why this specific conversion gets requested in the first place.

Real Complaints Behind Converting an LZ File to 7z

A documented, recurring pattern on 7-Zip's own SourceForge discussion forums involves people downloading a .tar.lz or plain .lz release and finding that stock 7-Zip doesn't recognize the extension at all, since lzip support isn't built into the standard release — the fix is either installing the separate Lzip7z plugin or converting the file to a format 7-Zip already understands natively, like 7z itself.

A second real issue is people expecting a meaningfully smaller file after converting, and being surprised when the .7z result comes out close to the same size as the original .lz file, sometimes even slightly larger with small archives. This isn't a conversion mistake — it's the direct consequence of both formats already compressing with the same LZMA family of algorithms, so there's little raw compression gain left to capture just by changing containers, unlike converting from a DEFLATE-based format where a real size drop is expected.

A third pattern shows up specifically with .tar.lz archives: because the whole archive is one continuous lzip stream wrapped around a tar layer, extracting a single file requires decompressing everything first, which some people don't realize until they're waiting on a large download just to grab one document — a limitation that disappears once the same content is rebuilt as a properly multi-stream 7z archive.

LZ and 7z Compared Directly

Questions About Converting an LZ Archive Into 7z

Will converting from LZ to 7z make the file noticeably smaller?
Usually not by much. Both formats already compress with LZMA-family algorithms, so most of the size difference between them comes from container overhead and 7z's optional solid compression, rather than a jump in raw compression strength.

Why doesn't 7-Zip open my .lz file directly if it already uses LZMA?
Because 7-Zip's standard build reads its own 7z container format and a handful of others, but lzip's specific container — with its magic bytes, version byte, and 3-factor trailer — isn't among them without the separate Lzip7z plugin installed.

Does 7z give me the same integrity protection as LZ?
Not identically. 7z checks its internal streams with individual CRC32 values, while lzip's trailer combines a CRC32, the original data size, and the compressed member size into what its own documentation calls a 3-factor check.

Can I password-protect the 7z file after converting?
Yes. 7z supports AES-256 encryption, including an option to encrypt the file listing itself so filenames stay hidden without the password — a capability lzip's format has no equivalent for at all.

Is a .tar.lz file handled differently than a plain .lz file in this conversion?
Yes. A plain .lz file holds one compressed stream; .tar.lz wraps a tar archive of multiple files inside that stream. Converting either to 7z means decompressing back to the original files and rebuilding them as 7z's native multi-file structure.