A zip file is already compressed, so you cannot compress it further without losing data

A zip file is a container that holds other files in a compressed format. Once you create a zip, the files inside it are already as small as the zip format can make them. Trying to compress a zip file again — by putting it inside another zip — does not make it smaller. Instead, you end up with a file that is slightly larger, because you have added a second layer of compression overhead.

If you have a zip file and you want to make it smaller, your real options are limited. You can delete files you no longer need from inside the zip, move the zip to cloud storage so you do not have to email it, or split it into multiple smaller zips. But you cannot compress the zip itself without accepting data loss or using a specialized tool that is rarely worth the trouble.

Key Takeaways

  • Zip files are already compressed; putting a zip inside another zip makes it slightly larger, not smaller.
  • If you need to make a zip file smaller, delete unnecessary files from inside it or split it into multiple zips instead.
  • Some file types inside a zip (like photos or videos) are already compressed and will not shrink further no matter what you do.
  • Cloud storage or file transfer services are often better than compression when you need to send a large zip to someone else.

Why zipping a zip file does not work

When you create a zip file, the compression algorithm scans each file for patterns and redundancy, then removes the repetition. A text document might shrink to 20 percent of its original size. But once that work is done, there is very little left to compress. The second zip sees a file that is already tightly packed and has almost nowhere left to trim.

In practice, zipping a zip file usually makes it 1 to 3 percent larger. You have added the overhead of a second compression layer — extra metadata, headers, and structure — without gaining any real space savings. The only exception is if the original zip file was created with very old or inefficient compression settings, but even then the gain is negligible.

How to actually make a zip file smaller

If you have a zip file that is too large, the most direct approach is to remove files you do not need. Open the zip in your file manager (Windows, Mac, and Linux all let you open zips like folders without special software). Delete any files that are outdated, redundant, or no longer necessary. Then save the changes. The new zip will be noticeably smaller.

If you need to keep all the files but still reduce size, split the zip into multiple smaller zips. Most file managers and dedicated zip tools (like 7-Zip on Windows or The Unarchiver on Mac) have a "split archive" feature. You specify a maximum size — say, 100 MB per file — and the tool creates multiple zips that you can send or store separately. The recipient can combine them back into one zip later.

Another option is to check what is actually inside the zip. Some files compress well; others do not. Photos, videos, and audio files are usually already compressed by their own format (JPEG, MP4, AAC). Including them in a zip saves almost no space. If your zip is mostly media files, compression is not the problem — you straightforward have a lot of data. In that case, cloud storage or a file transfer service is usually faster and easier than trying to shrink the file itself.

When you might need to re-compress a zip

There are rare situations where you might extract a zip, modify the files inside, and then re-zip them. For example, if you downloaded a zip of documents, edited a few of them, and want to send the updated versions back to someone, you would extract, edit, and create a new zip. But this is not compression — it is creating a fresh archive from modified files.

If you are working with very large zips and need to squeeze out every possible byte, specialized tools like 7-Zip or WinRAR offer compression settings you can adjust. You can choose a higher compression level (which takes longer but produces a slightly smaller file) or switch to a different compression algorithm. But the gains are usually small — often just a few percent — and the time cost is usually not worth it unless you are archiving data you rarely access.

Sending large zip files to other people

If your zip file is too large to email, compression is not the solution. Email services typically reject attachments larger than 20 to 25 MB, and no amount of re-zipping will change that. Instead, use a file transfer service. Google Drive, Dropbox, OneDrive, and WeTransfer all let you upload a file and share a link. The recipient downloads from the link rather than receiving an attachment. This works for files of any size (up to your storage limit) and is usually faster than trying to compress.

If you are sending the zip to someone who needs to use it on an older computer or a phone, ask them what device they are using before you compress. Some older phones and tablets cannot open certain zip formats or handle very large files. In those cases, it is better to send individual files or use a service that lets them read one file at a time.

File types that do not compress well

Understanding what is inside your zip helps you decide whether compression is worth trying. Text files, spreadsheets, and documents compress very well — often to 10 to 30 percent of their original size. But photos (JPEG, PNG), videos (MP4, MOV), and audio (MP3, AAC) are already compressed by their own format. Putting them in a zip saves almost nothing.

If your zip is mostly photos or videos, the file size is not a compression problem — it is a data volume problem. You have a lot of media, and no amount of zipping will change that. Your options are to delete files you do not need, split them across multiple zips, or use cloud storage instead of trying to send them as a single file.

Frequently Asked Questions

Can I compress a zip file to make it smaller for email?

No. Zipping a zip file makes it slightly larger, not smaller. If your zip is too large to email, use a file transfer service like Google Drive or WeTransfer instead. These services let you upload the file once and share a link, which works for files of any size.

What if I delete files from a zip — does that make it smaller?

Yes. Open the zip in your file manager, delete the files you no longer need, and save. The new zip will be noticeably smaller. This is the most direct way to reduce a zip file's size.

Should I use a different compression tool like 7-Zip or WinRAR?

Only if you are archiving data you rarely access and want to squeeze out a few extra percent of space. For everyday use, the built-in zip tools in Windows, Mac, and Linux are fine. Specialized tools offer more control but rarely produce dramatically smaller files.

Why are my photos still taking up so much space in a zip?

Photos are already compressed by JPEG or PNG format. Putting them in a zip saves almost no space. If your zip is mostly photos, the large size is not a compression problem — you straightforward have a lot of image data. Consider splitting the zip into smaller files or using cloud storage.

Can I split a large zip into smaller pieces?

Yes. Most file managers and zip tools have a "split archive" feature. You specify a maximum size per file, and the tool creates multiple zips. The recipient can combine them back together later using the same tool.