ZIP is for bundling, not usually for shrinking

This surprises people, so it is worth stating plainly. Zipping a folder of photos, videos, MP3s or PDFs will save you almost nothing — often under two percent. Those formats are already compressed, and there is no redundancy left for ZIP to squeeze out.

What ZIP genuinely solves is the other problem: turning forty separate attachments into one. Most email clients, forms and messaging apps make sending a single file easy and sending forty files painful.

When zipping does shrink things

ZIP works by spotting repetition, so it performs well on anything stored as plain, uncompressed data:

Very well — text, CSV, JSON, XML, log files, source code, and uncompressed images like BMP or TIFF. Savings of 70 to 95 percent are normal.
Reasonably — WAV audio, some older document formats, databases.
Barely at all — JPG, PNG, GIF, MP4, MOV, MP3, PDF, DOCX, XLSX, PPTX. All of these are compressed already.

If your folder is mostly photos and you actually need it smaller, tick the shrink option above. Reducing the photos first and then bundling them is what produces a real saving — zipping alone will not.

Splitting for email

Gmail caps attachments at 25MB and Outlook at 20MB. Rather than working out by hand which files fit together, choose a split size and the tool packs your files into as many parts as it takes, each one under the limit.

Each part is a normal, independent ZIP file. Whoever receives them can open each one on its own — there is no need to have all the parts present, which is the usual annoyance with the multi-volume archives that desktop software produces.

Questions

Are my files uploaded?

No. The archive is assembled inside your browser, on your device. Nothing is transmitted, which matters when you are bundling contracts, records or personal documents.

Can the recipient open it?

Yes. These are standard ZIP files. Windows, macOS, iOS, Android and Linux all open them without extra software.

Can I password-protect it?

Not here. ZIP's built-in password protection is weak by modern standards and would give false reassurance. For anything genuinely sensitive, use a tool built for encryption rather than a ZIP password.

Why is my ZIP the same size as the originals?

Because the files inside were already compressed. This is normal and not a fault. You have still gained the thing you came for, which is one file instead of many.