How do I compress or zip files?

A zip does two things: it makes files smaller, and it turns many files into one. Most of the time it is the second that people actually want.

Safety

Step by step

1. Zip on Windows.Select the files or folder, right-click, then Compress to ZIP file. It appears alongside the originals, which are untouched. Rename it before sending.
2. Zip on a Mac.Select the items, right-click and choose Compress. One item keeps its name; several become Archive.zip, which is worth renaming.
3. Unzip on Windows.Right-click and Extract All, then choose where it goes. You can browse inside a zip without extracting, but editing files in there does not reliably save changes — extract first.
4. Unzip on a Mac.Double-click. It extracts into the same folder. There is no separate step.
5. Know what compresses and what does not.Documents, spreadsheets, text and uncompressed images shrink substantially. JPEGs, MP3s, MP4s and PDFs are already compressed and will barely change — zipping a folder of photos is about bundling, not size.
6. Use it to bundle rather than to shrink.One attachment instead of forty, with the folder structure preserved. That is the everyday reason to zip something.
7. Check the size limit you are sending into.Most email is around 20 to 25MB. If the zip is still too big, a cloud link is the right answer rather than splitting the archive.
8. Recognise the other formats.7z and RAR compress better but need software to open — do not send them to someone who has not asked. Zip is the one everybody can open without installing anything.
9. Treat password protection realistically.Standard zip encryption is weak and the file names are often still visible. For genuinely sensitive material, use a proper encrypted container or a secure transfer service.
10. Never open an unexpected archive.Attackers use them because the contents get past filters. If you were not expecting it, do not extract it — particularly anything ending .exe, .scr or .js.
11. Keep the originals until it is confirmed.Zipping does not delete anything, but do not delete the originals until the recipient confirms the archive opened.
12. Use a folder inside the zip.Zipping a folder rather than loose files means everything lands in one place when extracted, instead of scattering across the recipient's Downloads.

Tips

• Zip a folder, not loose files. It saves the recipient from forty items landing in their Downloads.
• Photos and videos are already compressed. If you need them smaller, resize them — zipping will not help.
• Rename Archive.zip before sending it. Everyone receives files with that name.

Common mistakes

• Opening an unexpected zip attachment — Archives get past attachment filters because their contents are not scanned until extracted. It is a standard way of delivering malware.
• Relying on zip password protection for sensitive files — Standard zip encryption is weak and file names often remain visible. Use proper encryption or a secure transfer service.

If it doesn't work