Compress a ZIP in your browser
Drop an existing ZIP to rebuild it. Expect a real saving on stored text and sidecar junk, and almost nothing on a ZIP of JPEGs, PDFs or MP3s.
or browse your device. Everything is processed on this device
No ZIP to hand?
How to compress a ZIP
It is opened in memory. Loose files belong on Create ZIP, which reports uncompressed size against the new archive.
The default removes macOS and Windows sidecar files. Turn it off when you need a byte-for-byte list of entry names.
Stored text, CSV, JSON and source files are compressed. JPEGs, PDFs, MP3s and other already-compressed payloads are normally left stored.
If nothing smaller came out, you get your original file back. That is the honest result for a ZIP that was already packed well.
When compressing a ZIP is worth it, and when it is not
A ZIP is a container, not one kind of content. Each entry can be stored as-is or compressed with Deflate. A basic archive creator may store a text report uncompressed, leaving a large and easy saving for this page. A well-made archive may already have Deflated every useful byte, in which case rebuilding it saves a few kilobytes of headers or nothing at all.
JPEG, PNG, PDF, MP3, MP4, WOFF2 and nested archives carry their own compression. Putting Deflate around those bytes again usually saves nothing and can add overhead. Try harder is allowed to test them, but the writer automatically stores an entry whenever its Deflated version is larger.
If you have loose files rather than a ZIP, use Create ZIP. That page compares the files with the archive. This page compares ZIP with ZIP, which is the only comparison that means anything when the input is already an archive. Neither page extracts files.
ZIP compression FAQ
Why is my ZIP file not reducing in size?
Usually because the files inside are already compressed. JPEG, PNG, PDF, MP3, MP4 and similar formats have already thrown away or packed the repetition Deflate looks for, so wrapping them in another compression layer barely moves the number. Text, CSV, JSON, XML and source code shrink well. Pictures and PDFs generally do not.
Is compressing an existing ZIP even useful?
Yes, on a narrow set of archives: ones that stored text uncompressed, and ones that carry __MACOSX or Thumbs.db junk. On a ZIP of photographs the honest result is often a few kilobytes, or the original file back. This page would rather say that than pretend a second Deflate pass is image compression.
How do I reduce my ZIP file size?
Drop the ZIP here and leave Remove junk files on. Stored entries that benefit from Deflate are recompressed and macOS or Windows litter is removed. If the weight is pictures or PDFs, compress those payloads first, then pack the smaller files with Create ZIP.
Can I create a ZIP from several files or a folder?
Yes, on Create ZIP. That page keeps folder structure and compares the uncompressed files with the archive. This page only rebuilds an existing ZIP.
Does this unzip or extract files?
No. It reads an existing ZIP only to rebuild it as a smaller ZIP. It does not expose the entries for separate download.
What does Try harder do?
It asks Deflate to try every entry, even formats that normally do not benefit. The archive writer compares the result entry by entry and stores the original payload whenever Deflate is larger. It does not re-encode a JPEG or PNG, so there is no hidden quality loss and no reason to expect a dramatic gain.
Can it open an encrypted or Zip64 archive?
No. Password-protected ZIPs cannot be read without asking for and handling a password, and Zip64 is normally used for archives over 4GB or with more than 65,535 entries. Both are refused with a clear explanation rather than partly read and rebuilt into a broken file.
Are my files uploaded?
No. Reading, Deflate compression and ZIP writing all happen in this browser tab. There is no upload step and no account. The practical ceiling is the memory available on your device, because the archive and its entries have to be held while the new ZIP is written.
Related
Same format joins the queue. Anything else re-routes to its own tool.