How to reduce the size of a ZIP file

Why ZIP barely compresses anything

Lossless compression works by exploiting repetition. A text file, a CSV or source code is full of it: they easily lose 70 to 90% of their size.

JPEG photos, PNG images, MP3s, MP4s and recent PDFs have already been compressed, often lossily. Their data looks like random noise, with nothing left to factor out. A ZIP of photos typically saves 1 to 3%.

• Text, CSV, code, logs: 70 to 90% smaller
• Older Office documents (.doc, .xls): 50 to 80% smaller
• Recent Office documents (.docx, .xlsx): almost nothing, they are already ZIP files
• Photos, music, videos, PDFs: 0 to 3% smaller

Lever 1: remove what does not belong

This is the most profitable lever, and the most neglected one. Duplicates, raw video footage, intermediate exports, temporary files and installers often make up half of a personal archive.

The problem is that you cannot sort what you cannot see. Organizing the archive by file type instantly shows where the weight is: if the videos folder takes up 3 GB out of 4, you know what to do.

Lever 2: resize images

A photo from a recent smartphone weighs 4 to 8 MB. For email, a report attachment or a web gallery, a version 1,600 pixels wide is more than enough and drops below 500 KB.

Do it on a copy, never on your originals: this reduction cannot be undone.

Lever 2b: re-encode videos

In a personal archive, videos are almost always the biggest item: one minute shot in 4K on a recent smartphone easily exceeds 300 MB. No archive format will change that.

The lever is re-encoding. HandBrake, free and open source, converts a video to H.265 at visually similar quality, often cutting its size in half or more. Dropping from 4K to 1080p for simple sharing divides the size by another two to three. Again, work on copies.

Lever 2c: shrink PDFs

A PDF from a scanner or a layout program can weigh dozens of megabytes because of the images inside. On macOS, Preview offers a “Reduce File Size” Quartz filter when exporting, which is effective but can be rough on legibility.

PDF software and many online services offer finer compression levels. For confidential documents, prefer a local tool over an online service whose retention policy you do not know.

Lever 3: change archive format

7z with LZMA2 compression often saves 10 to 30% more than ZIP on documents and code. On photos or videos, the gain stays marginal: the nature of the content always matters more than the choice of algorithm.

The catch: the recipient must be able to open the format. Internally, that is often fine; for external sending, ZIP remains the safe choice.

Lever 4: split into several archives

When the total size cannot come down, you can still spread it out. One archive per year, per project or per type gets past attachment limits and recovers better after an interrupted transfer.

Sorting by date or by topic sets up exactly this split: each top-level folder becomes a standalone archive, with a name that says what it contains.

Where to start: the order that pays off most

Not all levers are equal, and order matters. Start with what degrades nothing and saves the most, finish with what requires trade-offs.

• 1. Make the weight visible: organize the archive by file type
• 2. Remove duplicates, intermediate exports and useless files
• 3. Re-encode videos, the biggest item in most cases
• 4. Resize photos meant for sharing
• 5. Split what is left into several topic-based archives

Attachment limits to know

Gmail caps attachments at 25 MB per message and Outlook.com at 20 MB, and many corporate mail systems are set lower. Beyond that, you need a file transfer service or a shared space.

Think about the recipient too: a download link is almost always more comfortable than a 2 GB archive sitting in an inbox.