How do I open a 7z file on iPhone?
You need an app with 7z support. The Files app can uncompress ZIP archives, but it does not offer that action for a .7z file. Convexy can both open and create real 7z archives entirely on your iPhone.
Why the Files app refuses
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.
Why Convexy can create 7z
7z is an open, documented archive format. Its LZMA and LZMA2 compression algorithms can be implemented in software, and Convexy's bundled archive library supports both reading and writing it.
The practical consequence is that Convexy can create a genuine 7z archive on your iPhone. It is not a renamed ZIP: it is a real LZMA2-compressed 7z that standard desktop 7z tools can open.
RAR is handled separately in Convexy. The app opens and extracts RAR archives but does not create them.
Why 7z files are smaller
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.
Why extracting one small file from a big 7z can be slow. Solid compression is the reason. Because the archive is one continuous compressed stream rather than a set of independently-packed files, pulling out a single file near the end may require decompressing everything before it. ZIP, which packs each file separately, can jump straight to the one you want. That is the trade: 7z gives you a smaller archive and slower selective extraction. On a phone, with less CPU and RAM than a desktop, you will feel it more.
7z encryption is genuinely good
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.
When a 7z will not open
- Multi-volume archives. Files named
archive.7z.001,archive.7z.002and so on are one archive split into pieces. You need all of them, complete, in the same folder. The.001on 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.
What Convexy does with 7z
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 real 7z archives compressed with LZMA2. Standard desktop 7z tools can open the result. Convexy 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.
How to do it
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Get the 7z into Files
Save it from Mail, Safari, Messages or wherever it came from. If it is a multi-volume set — .7z.001, .7z.002 and so on — download every part and keep them together in one folder.
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Open it in Convexy
Share the .7z into Convexy, or open Convexy and browse to it. No decoder to install and no server involved.
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Look inside first
Convexy lists the archive's contents so you can see what you are about to unpack before you unpack it.
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Extract
The archive is unpacked on your device. A large solid archive takes longer on a phone than on a desktop, which is the price of 7z's better compression. If it is password-protected you will be prompted.
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Or make one
To go the other way, pick your files and choose 7z as the output format. Convexy writes a genuine LZMA2-compressed archive that standard desktop 7z tools can open.
Common questions
Can the iPhone Files app open 7z files?
No. iOS supports ZIP only — long-press a .zip and Uncompress appears. A .7z has no Uncompress option, no preview and no thumbnail. You need an app with a 7z decoder built in.
Can I create a 7z file on an iPhone?
Yes. Convexy creates real LZMA2-compressed 7z archives entirely on-device. Standard desktop 7z tools can open the result.
Is 7z better than ZIP?
Usually smaller, sometimes dramatically so — LZMA2 uses a far larger search window than ZIP's Deflate, and 7z compresses files as one continuous stream so it finds redundancy between files, not just within them. Its encryption is also much stronger. ZIP's advantage is universality: every operating system opens a ZIP with no help, and iOS opens it natively.
Why is my 7z file so slow to extract on my phone?
Because of solid compression. A 7z is typically one continuous compressed stream rather than a set of independently packed files, so extracting a single file may require decompressing everything before it. LZMA2 also needs significant memory and CPU for large dictionaries. That is the price of the better compression ratio, and a phone feels it more than a desktop does.
Is 7z encryption secure?
Yes, when used with a strong password. 7z uses AES-256 with a properly derived key, and it can encrypt the file list as well, so nobody can even see what is in the archive without the password — something ZIP cannot do. Note that ZIP's original legacy encryption is broken and offers effectively no protection. As always, AES-256 with a weak password protects nothing.
Why can I create a 7z but not a RAR?
Convexy's archive writer supports 7z, ZIP, TAR, GZ, BZ2, TAR.GZ and TAR.BZ2. Its bundled archive library reads RAR but does not provide RAR writing, so RAR remains extract-only in Convexy.