Convert TGZ to 7Z Online (Replacing DEFLATE With LZMA2 on the Same Tar Data)

What Gets Unwrapped Before a 7Z Archive Can Be Built

A TGZ file is a tar archive — files bundled with 512-byte header records, a layout unchanged since Seventh Edition Unix in 1979 — compressed as a single continuous stream using gzip, released in 1992 by Jean-loup Gailly and Mark Adler. A 7Z file is a completely different container, created by Igor Pavlov for the 7-Zip project and first released in 1999, built around the LZMA algorithm rather than gzip's DEFLATE, and structured with its own internal header describing every file, folder, and compression setting used.

Converting TGZ to 7Z means decompressing the gzip layer to expose the raw tar stream, then unpacking that tar structure into its individual files, and finally re-bundling those same files inside a new 7Z container using LZMA2, the improved variant of LZMA that 7-Zip has defaulted to since version 9.20. The files themselves don't change; only the archive format and compression algorithm wrapped around them do.

One structural detail carries over cleanly regardless of the algorithm swap: tar's own header format records each file's Unix permission bits, owner, and group directly, and once those files are unpacked from the tar stream, a 7-Zip build that supports Unix attributes can preserve that same metadata inside the new archive. Whether it actually does depends on the specific tool and settings used for the conversion, since 7Z's own specification treats this metadata as an optional extra field rather than a mandatory part of every entry.

Why LZMA2's Dictionary Is the Real Source of the Size Difference

Gzip's DEFLATE algorithm looks for repeated byte sequences within a fixed 32 KB sliding window, a limit that was reasonable for the memory available when DEFLATE was designed in the early 1990s but is tiny by current standards. LZMA2 uses a dictionary that can scale up to 64 MB or more depending on the compression level chosen, letting it spot repetition across a far larger span of the data than DEFLATE ever can, which is the direct, mechanical reason 7Z archives so often come out noticeably smaller than the equivalent TGZ.

LZMA2 also uses range coding for its entropy-coding stage rather than DEFLATE's Huffman coding, which generally represents probability distributions more precisely and squeezes out a further, smaller improvement on top of the dictionary-size advantage. Both differences are measurable and consistent, not marketing claims: the same source-code archive compressed both ways will show 7Z coming out smaller in the overwhelming majority of cases, at the cost of using noticeably more memory and CPU time during compression to search that much larger dictionary.

7-Zip also applies solid compression by default across every file inside the archive, similar in spirit to how gzip already treats a tar stream as one continuous run — the difference is 7Z's much larger dictionary makes that solid compression far more effective across a bigger set of files than gzip's 32 KB window ever could reach.

7-Zip's compression level settings, ranging from "Store" (no compression at all) up through "Ultra," also let the dictionary size and search depth be tuned explicitly, something gzip's own simpler -1 through -9 flags don't offer nearly as much control over, since DEFLATE's window size stays fixed at 32 KB no matter which of those numbered levels gets chosen. This extra tuning range is part of why two different TGZ-to-7Z conversions of the same files, using different 7-Zip settings, can produce noticeably different output sizes even though both are still, technically, LZMA2-compressed 7Z archives.

What Rebuilding as a 7Z Archive Gains and What It Costs

• Gain — a meaningfully smaller file on most content: LZMA2's larger dictionary and range coding typically outperform gzip's DEFLATE by a real, measurable margin.
• Lose — much of gzip's compression speed: searching a multi-megabyte dictionary takes substantially longer than DEFLATE's 32 KB window, so 7Z compression is noticeably slower.
• Gain — optional strong AES-256 encryption: 7Z supports encrypting both file contents and filenames directly in the format, something a plain TGZ has no equivalent for at all.
• Lose — native macOS Archive Utility support: Apple's documented list of natively supported formats includes .tgz directly but not .7z, so opening a 7Z on a Mac requires a separate tool like The Unarchiver or Keka.
• Unchanged — Unix file permissions, if the conversion tool preserves them: 7-Zip can store Unix ownership and permission attributes, though whether a specific conversion tool actually writes them depends on that tool's own settings.

Which Platforms Open Each Format Without Extra Installation

TGZ has an advantage in built-in support: Apple's own documented Archive Utility feature list names .tgz directly, and Linux distributions universally ship gzip and tar as part of the base system, so a TGZ opens with nothing extra installed on either platform. 7Z has no equivalent built-in support anywhere — not in Windows File Explorer, not in macOS Finder or Archive Utility, and not by default in most Linux distributions' base install, since the 7-Zip project's own p7zip or the newer 7-Zip for Linux package has to be installed separately.

Windows needs 7-Zip itself, WinRAR, or another third-party tool to open either format, since File Explorer's own built-in archive support only covers ZIP. Once 7-Zip is installed, though, it opens 7Z natively as its own format and also reads TGZ without issue, making it a practical single tool for handling both sides of this specific conversion on Windows.

Linux distributions generally include tar and gzip in their base install, which is why every mainstream distribution can decompress a TGZ with tools already present, but p7zip or the newer 7-Zip package still needs to be installed separately through the system's package manager before a 7Z archive can be created or opened there, since 7-Zip's format isn't part of the standard base toolset the way tar and gzip are.

The Documented Reasons This Particular Conversion Comes Up

A frequently discussed scenario on file-sharing and backup forums involves needing to shrink a large TGZ backup or dataset as much as possible before uploading it somewhere with a strict size cap or slow connection, where the meaningful size reduction LZMA2 offers over DEFLATE is worth the extra compression time, especially for a one-time archival task rather than a repeated build step. Because this is usually a one-off action rather than something repeated on every build, the slower compression time matters far less than it would in an automated pipeline running the same step hundreds of times a day.

A second real pattern involves wanting encryption that a TGZ simply doesn't offer natively — gzip has no built-in password protection mechanism at all, while 7Z supports AES-256 encryption of both file contents and, optionally, filenames, making it a documented upgrade path specifically for anyone needing to add password protection to an archive that previously had none. A third scenario shows up around software distributed for Windows specifically, where 7Z is a familiar, commonly expected format among Windows users already running 7-Zip, while a bare TGZ can read as unfamiliar or suspicious to someone without a Unix background.

DEFLATE's Small Window Set Against LZMA2's Larger Dictionary

Common Questions About Moving a Gzip Tarball Into 7-Zip's Format

Will a 7Z of the same files always be smaller than a TGZ?
Usually, but not guaranteed. LZMA2's larger dictionary and range coding generally outperform gzip's DEFLATE, though on data that's already tightly compressed, such as photos or video, the difference can be small or negligible.

Why does compressing to 7Z take so much longer than gzip did?
LZMA2 searches a dictionary that can be thousands of times larger than DEFLATE's fixed 32 KB window, and that larger search space is directly why 7Z compression takes noticeably more time and memory.

Can I password-protect a 7Z the way I couldn't with my TGZ?
Yes. 7Z supports AES-256 encryption for both file contents and filenames as a built-in option, while gzip has no password-protection mechanism of its own at all.

Does my Mac open 7Z files the same way it opens TGZ files?
Not natively. Apple's own documented Archive Utility feature list includes .tgz but not .7z, so opening a 7Z on macOS requires installing a separate tool such as The Unarchiver or Keka.

Is 7-Zip's compression really that much stronger than gzip's?
On most real-world data, yes, and the gap is measurable rather than marketing language: LZMA2's dictionary can reach tens of megabytes compared to DEFLATE's fixed 32 KB window, letting it find far more repetition to compress away.