Convert RAR to 7Z

The usual reason to convert a RAR is that nothing opens it, and the usual answer is ZIP — which works, and makes the archive bigger, because ZIP compresses every entry separately. For a collection you are keeping rather than sending, that is a poor bargain repeated across every file.

7Z is the other answer, and it is the one that suits a collection. It keeps the property that makes RAR small in the first place, it costs nothing to implement, and the tools that read it are free, actively maintained and available on every platform. This is the conversion for somebody tidying a shelf rather than answering an email — the aim is that in ten years the archives still open, without a licence, a download from a single vendor, or a version of Windows that has since been retired. That is a different goal from compatibility today, and it leads to a different format.

Our registry marks both RAR and 7Z as solid. A solid archive concatenates its members into one stream before compressing, so material shared between files is stored once and referenced afterwards — the reason a folder of two hundred similar documents collapses so far in either format.

7Z adds an LZMA2 dictionary of up to 64 MB on top of that, meaning the compressor can reference material tens of megabytes earlier in the stream rather than a few kilobytes back. Which of the two ends up smaller on any particular archive depends on the content and on the settings the original was written with, and the difference is usually small enough that it should not drive the decision either way. That is the useful conclusion here: unlike the move to ZIP, this conversion does not ask you to accept a materially larger file as the price of leaving a proprietary format behind.

RAR is proprietary in our registry's terms and 7Z is open, and for an archive you intend to still open in fifteen years that distinction is the whole point. An open specification means the format can be implemented by anyone, which is why 7-Zip, Keka and PeaZip all read 7Z, and why nobody has to negotiate with a company to write a reader.

It also removes a licensing question from your own storage. RAR's creation tool is commercial software, so a collection kept in RAR quietly assumes that a paid product continues to exist, to be sold, and to run on whatever machine you own in fifteen years. A 7Z archive assumes only that free software still compiles, which is a considerably safer bet and one you can act on yourself if it ever stops being true.

This conversion works and its mirror image does not, and the reason is legal rather than technical. The UnRAR licence permits using the code to extract archives and specifically forbids using it to build a program that creates RAR files, so producing one is the single thing our converter may not do.

It is enforced in three places rather than remembered in one: the format is marked unwritable in the registry, the converter's list of formats it is allowed to write does not contain RAR, and a test fails if the two ever disagree. The extraction itself uses `unrar-free`, which is GPL-2+ and in Debian's main archive, run as a separate process — Debian builds 7-Zip without the RAR codec, so RAR takes a different path here than any other archive format.

A recovery record is the notable one. RAR can store parity data inside the archive so that a damaged file can repair itself, and there is nothing equivalent in 7Z — if that redundancy is why you chose RAR, converting removes it silently.

The general rule for archive pairs here covers the rest: every member comes out byte for byte, and what is at risk is what the container knew about the files rather than what was in them. A password, and on some formats the permissions and timestamps. If a recovery record matters to a particular archive, keep the RAR beside the 7Z rather than replacing it.

Both formats support strong encryption and neither can be repacked while it is in force. The extractor is invoked in a way that fails immediately on a protected archive rather than blocking on a password prompt — there is no terminal on the converter for one to appear in, and a job that hangs until it is killed tells you less than a job that refuses at once.

With the password in hand the local route is short: extract the RAR, then compress the folder to 7Z with 7-Zip or Keka and set a new password there. 7Z's encryption also covers the file names, which RAR only does optionally — a genuine improvement that is worth the extra step for anything sensitive.

RAR normalised multi-volume archives — `part1.rar`, `part2.rar`, or the older `.r00` chain — because it was designed when files travelled on removable media. Extracting one requires every volume present at the same moment.

This converter is handed a single uploaded file, so a set cannot be rejoined even if you start with the first part; the extractor finds the archive incomplete and the job fails. Reassemble the volumes with a local archiver first, or ask the source for a single file. It is a property of the arrangement rather than a defect, and it is cheaper to know now than after four uploads.

This pair runs on our converter rather than in your browser. The archive is uploaded over an encrypted connection, extracted with unrar-free, packed again as a 7Z from inside the extracted directory, and returned; everything the job wrote is deleted when it finishes.

The scratch space is a bounded memory-backed filesystem and it is discarded with the container that ran the job. The free tier accepts 25 MB per file, jobs are killed at sixty seconds, and an archive declaring more than 2 GB of unpacked content is refused before extraction starts. For a whole collection rather than one file, 7-Zip does the same job locally with no ceiling at all.

Converting away from RAR does not make the archive openable by everyone, and it would be dishonest to imply otherwise. Our registry lists patchy support as a known problem for 7Z exactly as it does for RAR, and it is accurate: neither Windows Explorer nor the macOS Finder reads a 7Z without help, so a recipient with a locked-down machine is no better off than before. What changed is that the software they would need is free and available rather than commercial.

So treat 7Z as a keeping format and ZIP as a sending format, and keep the two decisions apart. If a file in the collection later has to go to a person, convert that one file to ZIP at that moment and accept the size for that one journey. Choosing your storage format for the storage case and translating on demand is a far better arrangement than compressing an entire archive for a recipient who may never exist, and it costs nothing until it is needed.

Most people who want this pair do not have one RAR; they have a directory of them going back years. A web converter is the wrong shape for that job — one upload at a time, 25 MB each, and no way to keep the results organised as they come back. The page is here for the file you need today, not for an afternoon of batch work.

For the whole shelf, 7-Zip on the desktop reads RAR and writes 7Z with no size limit and no upload, and it can be driven from a script so the whole set is processed in one pass with consistent settings. The one thing worth deciding before you start is whether to delete the originals: repacking is lossless for the file contents and does not carry a recovery record across, so keeping the RARs until the new archives have been tested costs disk space and buys certainty.