ZIP to 7Z

Convert ZIP to 7Z online: re-compress ZIP archives with 7z LZMA compression for smaller files. Free, private, no upload, works on any device.

Files are processed in your browser and never uploaded.

How to convert ZIP to 7Z

  1. Choose a .zip file with Choose a file or drop it onto the box above. ZIP-based files such as .jar, .apk and .epub are accepted too.
  2. If the ZIP is password-protected, enter the password in Password (only if the archive is encrypted). Otherwise leave it blank.
  3. Click Convert to 7Z. The ZIP is unpacked and its files are recompressed with LZMA.
  4. Click Download. The archive keeps its name and gets a new extension: reports.zip becomes reports.7z.

zip.js reads the ZIP and libarchive (WebAssembly) writes the 7Z, both inside your browser. The archive and its password stay on your device.

Why 7Z is often smaller than ZIP

Most ZIP files use Deflate, an algorithm from the early 1990s that looks back over a window of only 32 KB when searching for repeated data. LZMA, the method 7Z uses, searches a far larger dictionary and models the data more precisely. On content with lots of redundancy, such as text documents, source code, spreadsheets, logs, databases and uncompressed images, the 7Z version of an archive is usually clearly smaller than the ZIP.

The gain shrinks or disappears for data that is already compressed. JPEG and HEIC photos, MP4 videos, MP3 audio and modern Office files (which are themselves ZIP containers) leave little for LZMA to find, so converting an archive full of them saves little space. If your ZIP was created with "Store (no compression)", on the other hand, the difference can be substantial.

Trade-offs to weigh

The smaller file comes at a cost in compatibility. Windows 10, many online services and some phones cannot open 7Z without an extra app, while a ZIP works almost everywhere. Converting is a good idea for your own long-term storage, for uploads where bandwidth or quota matters, or when the recipient already uses 7-Zip.

Also note what the new archive does not contain:

  • Original modification dates are not stored in 7Z files created here; extracted files may show 1970 or no date.
  • Encryption is not carried over. Even if the ZIP had a password, the 7Z is written without one.
  • Empty folders are not included, and macOS junk entries (__MACOSX/ and ._ files) are skipped.

Tips

  • Building a 7Z from loose files or folders rather than a ZIP? Use Create 7Z.
  • If the recipient struggles to open the 7Z, they can turn it back into a ZIP with 7Z to ZIP.
  • When dates must be kept but you still want strong compression, convert to TAR.XZ in the Archive Converter.
  • For a ZIP that needs only a password, not a format change, see Password Protect ZIP.

Frequently asked questions

How much smaller will my archive get?

It depends entirely on the content. Text-heavy archives often shrink noticeably, while archives of photos or videos barely change. Compare the downloaded size with the original to see the result for your data.

Can I add a password to the 7Z?

Not with this converter; the output is unencrypted. If you need protection, keep a ZIP and use Password Protect ZIP with AES-256.

Does an encrypted ZIP work as the source?

Yes. Enter its password and the files are decrypted in your browser before being packed into the 7Z.

Is there a size limit?

The ZIP is processed in memory. Up to around 700 MB is comfortable, larger files are slower, and anything over 2 GB is refused.

Copied to clipboard