Convert TAR.GZ to 7Z Online (Replacing the Tar Container Entirely)

TAR.GZ Pairs Two Programs; 7Z Was Designed as One

A TAR.GZ file is the layered product of two independent programs that know nothing about each other: tar writes files into 512-byte header-and-data blocks with no compression logic of its own, and gzip compresses whatever continuous stream tar produces. 7-Zip's native 7z format, released by Igor Pavlov in 1999, was built the opposite way — as a single container format with its own internal index of file names, sizes, attributes, and compressed-data locations, so it never needed a separate archiving step bolted on before compression could happen.

Converting from TAR.GZ to 7Z means fully decompressing gzip's DEFLATE stream back into the plain tar byte sequence, then reading that tar structure to recover each file's name, size, and Unix permission bits, and finally re-encoding those same files inside 7z's own container using its default LZMA or LZMA2 compression. The Unix ownership and permission metadata that tar's headers carry doesn't automatically map onto anything in 7z's own attribute fields, since 7z's format was designed primarily around Windows file attributes rather than Unix mode bits — a real, documented gap depending on which specific tool performs the conversion.

A 32 KB Search Window Meeting a Dictionary Measured in Gigabytes

DEFLATE, gzip's compression algorithm formally specified in RFC 1951, can only look back up to 32 KB into the data it has already processed when searching for repeated byte sequences to reference. LZMA2, 7z's default algorithm, supports a dictionary size configurable up to 1,536 MB (1.5 GB) in the reference 7-Zip implementation — tens of thousands of times larger than DEFLATE's fixed window. On highly redundant data spread across a large archive, such as many similar log files or repeated boilerplate across source files, that gap translates directly into a smaller output file, since LZMA2 can find matching patterns far outside the range DEFLATE is structurally able to see at all.

That larger dictionary comes with a real cost: LZMA2 compression at high settings uses substantially more memory and CPU time than DEFLATE, particularly at 7-Zip's higher numbered compression levels, which increase the dictionary size and search effort together. DEFLATE remains markedly faster in both directions, which is a large part of why gzip stayed the default for so many build and packaging tools even as 7z's compression ratio pulled ahead on many kinds of data.

7z also supports solid-block compression the same way tar-plus-gzip already does — compressing multiple files together as one continuous stream rather than independently — but adds an option TAR.GZ has no equivalent for: splitting that solid compression into separate, sized blocks specifically to trade some ratio for the ability to extract a subset of files without decompressing the entire solid block first.

7-Zip's default settings also apply a filter pass ahead of LZMA2 for certain recognized file types, such as x86 executables, which rearranges relative branch instructions to make them compress more consistently. DEFLATE has no equivalent filter stage of any kind; it applies the same LZ77-and-Huffman process uniformly regardless of what kind of data it's compressing, which is one more reason the two algorithms land at different compression ratios on the same input even before dictionary size is factored in.

What Moving Off the Tar-Plus-Gzip Pair Gains and Costs

• Gain — a noticeably smaller archive on most compressible content: LZMA2's much larger dictionary generally beats DEFLATE's compression ratio on typical text, source code, and mixed-file archives.
• Gain — AES-256 encryption as a built-in option: 7z supports encrypting both file contents and, optionally, the file list itself, something TAR.GZ has no native equivalent for at all.
• Lose — the tar layer's native Unix permission and ownership fields: 7z's own attribute system doesn't map those the same way, so some tools drop or approximate them during conversion.
• Lose — DEFLATE's compression speed: LZMA2 at higher settings is measurably slower to compress, a real trade for archives built or rebuilt frequently.
• Gain — a single-file index for random access: 7z's central file table lets a compatible tool list or extract one entry without necessarily decompressing everything ahead of it, unlike gzip's single continuous stream.
• Unchanged — the actual file contents: both formats use lossless compression, so every extracted file matches the original byte for byte regardless of which container it traveled inside.

Which Current Tools Read and Write Each Format Natively

7z is created and read natively by 7-Zip on Windows and by p7zip, its long-standing Linux and macOS port, along with PeaZip on all three platforms. TAR.GZ, by contrast, is native to essentially every Unix-like system through GNU tar's -z flag, and macOS's Archive Utility opens it directly, while Windows File Explorer has no built-in support for either format and needs 7-Zip, WinRAR, or PeaZip installed regardless of which of the two is involved.

One documented asymmetry worth knowing: 7-Zip's own file manager can open a TAR.GZ archive directly as a nested pair, decompressing the gzip layer and displaying the tar contents inside without a separate manual step, treating the two-layer format as effectively one operation from the user's side. Going the other direction, turning a 7z archive into a TAR.GZ, requires 7-Zip or p7zip to first extract the 7z's contents, since neither GNU tar nor gzip has any native understanding of 7z's LZMA-based container at all.

Command-line users on Linux and macOS also have the p7zip package specifically for this purpose, which exposes the same 7z engine as a "7z" or "7za" binary without needing the Windows-oriented graphical interface at all — a real, practical route for converting a TAR.GZ produced on a build server into 7z as part of an automated packaging step, without leaving the command line.

Real Complaints Reported When Switching Between These Two Formats

A recurring, documented issue involves Unix file permissions not surviving a TAR.GZ-to-7z conversion intact, since 7z's attribute handling wasn't originally designed around Unix mode bits the way tar's header format was — users restoring a backup archived this way sometimes find executable bits or specific ownership settings didn't come through, which is a real limitation of the target format rather than a bug in the conversion process itself.

A second common report involves the noticeably longer time a large TAR.GZ takes to convert into 7z at 7-Zip's higher compression settings, particularly the larger dictionary sizes, compared with how quickly the original gzip compression ran — this isn't a malfunction, it's the direct cost of LZMA2 searching a dictionary many times larger than DEFLATE's fixed 32 KB window.

A third pattern shows up specifically among Linux and Unix users distributing software: because 7z isn't installed by default on nearly as many systems as gzip and tar are, a project switching its release archives to 7z risks alienating users who expect to extract a tarball with tools already present on their system, without installing p7zip or a similar package first.

A fourth, more subtle report involves multi-volume 7z archives: 7-Zip supports splitting a 7z output into fixed-size numbered parts much like ZIP's own split-volume feature, and someone converting a single large TAR.GZ expecting an equivalent single-file result sometimes gets a set of numbered .7z.001, .7z.002 parts instead, simply because the conversion tool or its default settings applied a size limit without that being the intended outcome.

TAR.GZ's Two-Layer Design Set Against 7Z's Single Container

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

Will my archive get noticeably smaller after converting TAR.GZ to 7z?
Often, yes, especially on text-heavy or repetitive content, since LZMA2's dictionary can reach far beyond DEFLATE's fixed 32 KB window to find matching patterns gzip simply can't see.

Do Unix file permissions survive this conversion?
Not always reliably. 7z's attribute system wasn't built primarily around Unix mode bits, so some conversion tools preserve them imperfectly compared with tar's native header fields.

Why does converting to 7z take so much longer than the original gzip compression did?
LZMA2 searches a dictionary that can be over a thousand times larger than DEFLATE's window, which finds better matches but takes measurably more CPU time and memory to do it.

Can I open a 7z file on a system that only has tar and gzip installed?
No. Neither tool understands 7z's LZMA-based container natively; 7-Zip or p7zip needs to be installed separately first.

Does 7z support the same solid, whole-archive compression that TAR.GZ uses?
Yes, and it goes further, letting solid compression be split into separate sized blocks so a subset of files can be extracted without decompressing everything that came before them.