Convert TAR.7Z to TAR Online (Removing the LZMA2 Compression Layer)

Stripping LZMA2 Compression Back Down to a Bare TAR Stream

A .tar.7z file is a tar archive — files bundled using 512-byte headers that record name, size, Unix permissions, ownership, and symlink targets, a structure standardized as USTAR in POSIX.1-1988 — compressed afterward with 7-Zip's LZMA2 algorithm. Converting it back to plain .tar means removing only that outer LZMA2 compression layer and leaving the tar stream underneath exactly as it was before compression was ever applied, byte for byte.

This is a genuinely simpler operation than converting to most other destination formats, since nothing about tar's own header structure, its file entries, or the metadata recorded in each header needs to change at all — the tar stream that comes out the other side is identical to the one that went into 7-Zip's compressor in the first place.

This makes TAR.7Z-to-TAR a genuinely different kind of operation than any conversion between two different container formats. It's purely a decompression step, not a rebuild — nothing about how files are organized, named, or described in the archive changes, only whether an LZMA2 compression layer sits on top of that unchanged structure or not.

Why This Conversion Only Removes One Layer, Not Two

LZMA2 compresses the entire tar stream as one undifferentiated sequence of bytes, without any awareness of tar's internal header and data-block boundaries. That separation is exactly what makes decompressing the 7z layer alone sufficient to recover a fully valid, complete tar file — there's no second transformation needed, since tar's own structure was never touched or reinterpreted by the compression step in the first place, unlike, say, converting to ZIP, which requires rebuilding each entry into a genuinely different container format.

The resulting plain .tar file will be noticeably larger than the original TAR.7Z, since LZMA2's dictionary-based compression, which can reach into the gigabytes for its reference window, is precisely what was responsible for the size reduction in the first place — removing it restores the tar stream to its full, uncompressed size, plus the 512-byte header and padding overhead tar itself always carries.

How much bigger the result gets depends on what compressed well in the first place. A TAR.7Z built mostly from source code or text-based configuration files, where LZMA2's wide dictionary found substantial repetition to exploit, expands considerably once decompressed. A TAR.7Z built mostly from already-compressed media, where LZMA2 achieved little reduction to begin with, changes size far less noticeably when the compression layer comes off.

What Decompressing TAR.7Z Back to Plain TAR Gains and Costs

• Gain — instant, sequential readability without a decompression step later: a plain tar stream can be read directly by any tar-aware tool without first running it through an LZMA2 decoder.
• Gain — every piece of tar's own metadata stays exactly as recorded: Unix permissions, ownership, and symlink targets in the header are completely unaffected, since only the outer compression layer is being removed.
• Gain — universal support on Linux and macOS with zero extra tools: GNU tar and BSD tar both read plain TAR archives natively, without needing 7-Zip or p7zip installed at all.
• Lose — the size reduction LZMA2 was providing: the resulting file can be substantially larger, especially for text-heavy or structured content that compressed well under LZMA2's wide dictionary.
• Lose — faster transfer and storage efficiency: a larger, uncompressed file takes longer to upload, download, or copy across a network than the compressed original did.
• Lose — nothing about file content or metadata: since LZMA2 never touched tar's internal structure, decompressing it back to plain tar changes only the file's size on disk, not anything about what's inside.

Which Tools Can Decompress the 7Z Layer Without Touching the TAR Layer

7-Zip on Windows and p7zip on Linux and macOS both decompress the LZMA2 layer of a TAR.7Z directly, producing the underlying .tar file as their output without requiring any separate tar-specific processing step, since decompression alone is all this particular conversion actually needs. Both tools have supported LZMA2 decompression since the algorithm's introduction, and both are free and open-source, meaning this conversion carries no licensing cost regardless of platform.

Windows 11's 24H2 update added native File Explorer extraction support for .7z files directly, built on the open-source libarchive project, letting a user recover the plain .tar file with a simple right-click extraction rather than installing 7-Zip separately, though earlier Windows versions still need a dedicated tool like 7-Zip or PeaZip for this step.

GNU tar and BSD tar themselves don't handle LZMA2 decompression directly in most standard builds the way they handle gzip or bzip2 through built-in flags, so recovering the plain tar file from a TAR.7Z typically means running 7-Zip or p7zip first to strip the compression layer, then optionally handing the resulting .tar file to tar itself for any further extraction.

PeaZip, available free for Windows and Linux, offers the same LZMA2-decompression capability through its own graphical interface, letting a user extract the plain .tar file without touching a command line at all, which some people find more approachable than piping commands together through a terminal, even though the underlying operation is identical either way.

Real Problems Reported Reversing a TAR.7Z Back to an Uncompressed TAR

A common complaint on backup and storage forums involves someone decompressing a large TAR.7Z back to plain tar for editing purposes, then being surprised by how much larger the resulting file is compared to the compressed original — a direct, expected consequence of removing LZMA2's dictionary-based compression, not a sign anything went wrong during the conversion.

A second documented issue involves running out of available disk space partway through decompressing a very large TAR.7Z, since the operation temporarily requires enough free space for both the original compressed file and the much larger uncompressed tar output simultaneously — a real, practical constraint worth checking for before starting this conversion on large archives specifically.

A third recurring pattern involves a documented 7-Zip File Manager bug where decompressing certain tar-containing archives results in files reported as missing or with a size of zero, even though the same archive extracts correctly through the command-line tar tool on Unix — worth checking for specifically when this conversion produces an incomplete-looking result.

A fourth documented pattern involves someone expecting to edit or update the newly decompressed tar file directly and then recompress it back into a smaller archive later, only to find the recompression step takes just as long as building the original TAR.7Z did — a reminder that decompressing removes the LZMA2 layer entirely rather than leaving some reusable partial state that would make a later recompression faster.

TAR.7Z and Its Decompressed TAR Compared by Size and Speed

Questions About Converting TAR.7Z Back Into Plain TAR

Does converting TAR.7Z to TAR change any of the files inside?
No. This conversion only removes the outer LZMA2 compression layer; tar's own header structure and every file's data inside it stay completely unchanged, byte for byte, throughout the whole process.

Why is the resulting TAR file so much bigger than the original TAR.7Z?
Because LZMA2's dictionary-based compression, which can reference gigabytes of prior data to find repeated patterns, was responsible for shrinking the file in the first place — removing it restores the tar stream to its full uncompressed size.

Do I need extra software to decompress a TAR.7Z on Linux?
Yes, p7zip specifically, since GNU tar's standard build doesn't include built-in LZMA2 decompression the way it does for gzip or bzip2. p7zip handles removing the compression layer, after which tar itself can read the result directly.

Will Unix permissions and ownership survive this conversion?
Yes, completely. Since LZMA2 never interacts with tar's internal header structure, decompressing it back to plain tar leaves every permission bit, ownership value, and symlink target exactly as recorded, with no rebuild step touching that data at all.

Should I have enough free disk space before starting this conversion?
Yes. Decompressing a large TAR.7Z temporarily requires space for both the original compressed file and the much larger uncompressed tar output at the same time, which can be a real constraint on storage-limited systems.

Is there any reason to convert TAR.7Z back to plain TAR instead of leaving it compressed?
Yes, mainly for compatibility with tools or scripts that expect an uncompressed tar stream, or for environments where the extra step of running an LZMA2 decoder isn't practical, such as older embedded systems without 7-Zip or p7zip installed and available at all.