7z or ZIP: which one to send
7z compresses noticeably better and the person receiving it may not be able to open it. That trade decides almost every case, and the answer is usually not the efficient one.
Your archive tool offers both. One produces smaller files, the other produces files everyone can open. That is the whole decision, and the compatibility side wins more often than people expect.
What separates them
ZIP dates from 1989 and is universally supported. Every operating system opens it without software. Every upload form accepts it. Every email client understands it.
Its compression is adequate rather than good, and it compresses each file independently — which matters more than it sounds.
7z is newer, open, and uses LZMA2 compression. It typically produces files 20–50% smaller than ZIP on the same input, and considerably better than that on some content. It supports strong AES-256 encryption as standard, larger files, and solid compression.
Its problem is support. macOS cannot open 7z without extra software. Neither can Windows before version 11 — which added it fairly recently. Neither can most webmail previews, most mobile file managers, or a long tail of tools that accept archives.
Solid compression, which is where 7z gets its advantage
ZIP compresses each file separately. Two hundred nearly identical log files get compressed two hundred times, with no benefit from their similarity.
7z can treat the whole archive as one continuous stream, so repeated patterns across files are compressed once. For many similar files — logs, source code, documents from the same template — this produces dramatic differences. A folder of two hundred similar text files might be 40MB as ZIP and 8MB as 7z.
The cost of solid compression is that extracting one file may require decompressing everything before it. For an archive you will extract whole, that is irrelevant. For an archive people will pick single files out of, ZIP is friendlier.
When compression barely matters
Worth knowing before optimising: already-compressed content does not compress again.
JPEG, PNG, HEIC, MP4, MP3, and most modern office formats (.docx, .xlsx, .pptx are ZIP containers already) are compressed. Archiving them produces a file roughly the same size regardless of format.
So for a folder of photos or video, 7z's advantage is close to zero and you are choosing purely on compatibility — which means ZIP.
Where 7z earns its keep: text, code, logs, CSV, databases, uncompressed images like BMP or TIFF, and large sets of similar files.
The decision
Send ZIP when:
- You do not know what the recipient uses. This covers most cases.
- It is going to a client, a form, or anyone outside your team.
- The content is mostly photos, video or audio, where 7z gains little.
- It needs to be opened on a phone.
Send 7z when:
- The recipient has agreed they can open it.
- It is text, code or logs where the difference is large.
- It is for your own storage or backup.
- Size genuinely matters — an upload limit you are up against.
Ask for ZIP when you are on the receiving end and someone sends 7z without checking. It costs them ten seconds.
On encryption
If you are protecting contents with a password, 7z's AES-256 is strong by default.
ZIP is ambiguous: it supports both AES-256 and the ancient ZipCrypto, which is breakable. Both produce a .zip and nothing in Finder tells you which you have. If you use encrypted ZIP for something sensitive, confirm your tool produces AES.
Either way, send the password through a different channel than the archive.
RAR, briefly
You may also see RAR. It is proprietary — freely readable, licensed to create. That is why Mac tools extract RAR and essentially none create it. If a tool claims to make RAR on a Mac, look closely at what it is actually producing. For your own archives there is no reason to choose it over 7z.
What Ziploom does
Ziploom creates ZIP and 7Z, and extracts RAR, ZIP and 7Z with optional password support. It does not create RAR, for the licensing reason above — we would rather state that than imply otherwise.
It runs natively on Apple silicon. Before extracting anything it checks for unsafe paths, symbolic links, suspicious compression ratios, oversized jobs and available disk space — the last of which is the one that otherwise surfaces halfway through a large 7z extraction, since solid compression means you cannot always predict the unpacked size from the archive.
You choose how existing destinations are handled before anything is written, follow progress while it runs, and reveal the output in Finder.
Everything happens on your Mac: no accounts, analytics, advertising, telemetry or network features.