Convert RAR to 7Z Online (Extraction-Licensed Format Meets an Open One)

Why 7-Zip Can Open This File but Was Never Allowed to Build One Like It

7-Zip can open a .rar file because it includes RARLAB's own unRAR source code, licensed specifically for extraction. That same license explicitly states the code may not be used to develop a RAR-compatible archiver capable of creating new RAR archives — so 7-Zip's RAR support, no matter how it's compiled, stops at reading. Converting RAR to 7z is, in a real sense, the only direction 7-Zip is legally positioned to take a RAR archive: unpack it fully using the licensed extraction code, then rebuild the same files from scratch as a 7z archive, a fully open format 7-Zip's own author, Igor Pavlov, designed and documented without any equivalent licensing restriction.

That's a genuinely different relationship than most format conversions, where the same tool can typically read and write both formats freely. Here, one side of the conversion is something 7-Zip can only ever read, and the other is something it was actually built to create — the conversion direction itself is shaped directly by which side of RARLAB's license 7-Zip is standing on.

7-Zip's own developer has addressed this restriction directly on the project's official feature-request tracker: adding RAR-creation support is explicitly rejected there, with the stated reason being that the only legal way to produce a genuine RAR file is to purchase a WinRAR license, at which point the tool doing the creating would no longer be free software at all. That's not a technical limitation 7-Zip could code its way around — it's a deliberate legal boundary the project maintains on purpose.

RAR5's Proprietary Algorithm Against 7z's Openly Documented LZMA2

RAR5, the default format since WinRAR 5.0 in 2013, compresses using RARLAB's own proprietary algorithm with a dictionary size up to 4 GB — the exact internal workings of that algorithm are not published, since RARLAB doesn't release the format as an open specification the way it does with unRAR's extraction-only code. 7z's default compression method, LZMA2, is by contrast fully documented and open, an evolution of the original LZMA algorithm that adds better handling of incompressible data and multithreaded compression by splitting the input into independently compressed chunks.

Benchmarks comparing the two vary by content type and settings, and neither format wins outright on every kind of data — 7z's LZMA2 at high compression levels is well documented as generally aggressive on text and source code, while RAR5's larger dictionary and solid-archiving mode can pull ahead on batches of many small, similar files. The more consistent, verifiable difference isn't which one compresses smaller in every case; it's that 7z's method is openly specified and independently implementable, while RAR5's remains something only RARLAB's own licensed code actually executes.

7z also supports several alternate compression methods beyond LZMA2 within the same container, including PPMd and BZip2, selectable per archive depending on which one suits the content better — a plain text log file and a folder of already-compressed media benefit from genuinely different settings, and 7z's format lets that choice be made explicitly rather than relying on one fixed proprietary algorithm the way a RAR archive does.

What Rebuilding a RAR as a 7z Archive Gains and Loses

• Gain — a format 7-Zip can both read and write freely: 7z carries no licensing restriction like the one blocking 7-Zip from creating RAR files.
• Lose — RAR5's Reed-Solomon recovery record: 7z's own specification has no built-in equivalent for embedding error-correction data inside the archive itself.
• Gain — an openly documented compression method: LZMA2 is specified and implementable by anyone, unlike RARLAB's proprietary RAR algorithm.
• Lose — RAR5's optional filename encryption: 7z does support AES-256 for file contents, but hiding the file listing itself works differently between the two formats' header structures.
• Gain — solid-block compression that's independently implementable: 7z supports its own solid-archive mode, grouping files into compression blocks, without depending on one company's proprietary engine to create it.
• Lose — nothing about the actual file content: the underlying files extracted from the RAR come out byte-for-byte identical once rebuilt inside the 7z archive.

Where This Conversion Actually Runs Without Extra Software

7-Zip itself is the one program that already has everything this conversion needs built in on Windows: its file manager opens .rar archives directly through the bundled unRAR code and writes .7z archives through its own native, fully-owned LZMA2 implementation, so the entire RAR-to-7z process happens inside one application without needing WinRAR at any point. PeaZip, built on the same p7zip codebase that powers 7-Zip's command-line engine on Linux and macOS, offers the identical read-RAR/write-7z capability on those platforms.

7z archives open on Windows, macOS, and Linux wherever 7-Zip, p7zip, or Keka (on macOS) are installed, none of which are preinstalled by any operating system's file manager by default — unlike ZIP, 7z still needs a dedicated tool on every platform, it just doesn't need a specifically licensed commercial one the way creating a RAR archive from scratch would.

That distinction shows up clearly in server and automation contexts: a Linux build server can install p7zip freely and script 7z creation as part of an automated pipeline with no licensing step involved, while doing the equivalent with RAR would require either a Windows machine somewhere in that pipeline or a properly licensed copy of RARLAB's command-line tool, since no free, independently written RAR-creation engine is legally available to install instead.

Documented Complaints Specific to Moving RAR Content Into 7z

A recurring, documented question on 7-Zip's own support forums is why the program can open RAR files but has no option anywhere in its interface to save or create one — this isn't a missing feature the developers plan to add; it's a direct consequence of the unRAR license explicitly prohibiting RAR-creation code from being built on top of it, a restriction 7-Zip's own discussion threads reference directly when the request comes up.

A second common issue involves an encrypted RAR archive failing to open in 7-Zip at all during the first step of this conversion — the unRAR extraction code 7-Zip includes handles RAR5's AES-256 encryption, but the correct password still has to be supplied before any files can be pulled out, so the conversion to 7z can't proceed until the original RAR password is known, exactly as with any other password-protected archive.

A third pattern involves expecting the resulting 7z archive to carry over a RAR5 recovery record automatically — it can't, since 7z's specification has no comparable built-in error-correction feature; anyone relying on that protection for a converted archive needs a separate tool such as par2 to add equivalent recovery data after the fact.

A fourth issue shows up with multi-volume RAR archives specifically — a set of .part001.rar, .part002.rar files needs every volume present before 7-Zip can extract anything at all, since RAR5's splitting scheme spreads the archive's internal structure across the full set rather than keeping each volume independently readable; a conversion attempted with a volume missing simply fails rather than producing a partial result.

RAR's Closed Engine Set Against 7z's Open One

Questions About Turning a RAR Archive Into a 7z One

Why can't 7-Zip just save a RAR archive as a new RAR instead of converting it?
Because 7-Zip's RAR support is built on RARLAB's unRAR code, which is licensed for extraction only — the license specifically forbids using that code to create new RAR archives, regardless of how 7-Zip is compiled.

Does converting to 7z lose the RAR archive's recovery record?
Yes. 7z's specification has no built-in equivalent to RAR5's Reed-Solomon recovery record, so that specific protection doesn't carry over unless it's added separately afterward with a tool like par2.

Is 7z actually smaller than RAR for the same files?
It depends on the content. 7z's LZMA2 tends to do well on text and code, while RAR5's larger dictionary and solid mode can pull ahead on many small similar files — neither format wins in every case.

Can I convert a password-protected RAR to 7z without the password?
No. The archive has to be decrypted first using the correct password before any files can be extracted and rebuilt as a 7z, the same requirement as opening the RAR at all.

Is 7z actually free to create, unlike RAR?
Yes. 7z is an open format with no licensing restriction comparable to RAR's — 7-Zip, p7zip, and other tools can create it without any commercial license required.