How do I open a 7z file on iPhone?

iOS's built-in archive support is ZIP and only ZIP. Since iOS 13 you can long-press a file to Compress it into a .zip, and long-press a .zip to Uncompress it. That is the entire feature — it is not a general archive engine, and Apple has not extended it to any other format.

So a .7z sits in Files doing nothing: no preview, no Uncompress, no thumbnail. Same for RAR, TAR and everything else. To open one you need an app with a 7z decoder built in, which in practice means one built on libarchive or on the 7-Zip code itself.

This is the part worth knowing, because it changes what is possible.

RAR is proprietary. RARLAB publishes enough to decode RAR archives, but the encoder is reserved — no free RAR encoder exists, anywhere, on any platform. Nothing but WinRAR can create a RAR.

7z is the opposite. Igor Pavlov's 7-Zip is open source, the format is documented, and the compression algorithms behind it — chiefly LZMA and LZMA2 — are freely implementable. libarchive reads and writes 7z. Anyone can build a 7z encoder into an app without asking permission or paying anyone.

The practical consequence: your iPhone can genuinely create a 7z archive. Not a ZIP with a renamed extension — a real 7z, LZMA2-compressed, that 7-Zip and WinRAR on a desktop will open normally. That is a claim no honest app can make about RAR.

7z routinely beats ZIP, often substantially, and it does so for two reasons that are worth understanding because they also explain its downsides.

A much bigger dictionary. Compression works by spotting repetition. LZMA2 can look back across a huge window — many megabytes — to find a repeated sequence, where ZIP's Deflate is limited to a 32 KB window. Deflate literally cannot see a repetition that happened 100 KB ago. LZMA2 can, and exploits it.

Solid compression. ZIP compresses each file independently. 7z, by default, concatenates the files and compresses the whole stream as one continuous block. So if you archive 500 similar files — source code, log files, a folder of text documents — 7z spots the redundancy between the files, not just within each one. On collections like that, 7z can be dramatically smaller than ZIP, occasionally by a factor of several.

On a folder of JPEGs or MP4s, it will save you almost nothing. Those are already compressed, and there is no redundancy left for any algorithm to find. This is true of every archive format and is not a failing of 7z.

Another real advantage, and one people rarely know about.

ZIP's original encryption is broken — a 1990s scheme with practical attacks against it, and it should be treated as offering no protection at all. Modern AES-256 ZIP encryption exists, but support for it is inconsistent across tools, so you cannot rely on the recipient being able to open it.

7z uses AES-256 as standard, with a key derived from your password through many rounds of hashing, and it is implemented consistently across the tools that support the format. It also offers something ZIP cannot: encrypted headers, meaning the list of filenames is encrypted too. With an encrypted ZIP, anyone can see exactly what files are inside without the password. With a header-encrypted 7z, they cannot even see that.

As always, the encryption is only as good as the password. AES-256 with the password password1 protects nothing.

• Multi-volume archives. Files named archive.7z.001, archive.7z.002 and so on are one archive split into pieces. You need all of them, complete, in the same folder. The .001 on its own is a fragment and will not extract.
• It is password-protected. You need the password. There is no way round AES-256, and anyone offering you one is selling snake oil.
• Truncated download. Check the size against the source — a partial archive fails in ways that look like corruption, because it is corruption.
• It is very large and very solid. Not a failure so much as a wait. A large LZMA2 archive with a big dictionary needs real memory and CPU to unpack, and a phone has less of both than the machine that made it.

It extracts 7z archives on your device, and lets you preview the contents first so you can see what is inside before unpacking it.

It also creates 7z archives, compressed with LZMA2 — a real 7z that desktop 7-Zip and WinRAR will open. Because the format is open, this is something an iPhone app can honestly offer, unlike RAR. It can also create ZIP, TAR, GZ, BZ2, TAR.GZ and TAR.BZ2.

Everything happens on-device, so it works with the network off. And archive compress and extract are free forever — not part of the paid unlock, and they keep working after the trial ends.