gzip vs ZIP: they are not the same tool

People say “gzip it” and “zip it” as if they were synonyms. They share an algorithm, but they are built for different jobs.

Side by side

Same family, different container

Under the hood, everyday ZIP and gzip both speak Deflate (the same “find a repeated phrase, write a short pointer” method). gzip wraps one Deflate stream in a 10-byte header and an 8-byte footer with a checksum. ZIP wraps each file in its own header and keeps a table of contents at the end of the archive so you can jump to only-this.txt without inflating everything else.

Because ZIP compresses files one at a time, it cannot share a dictionary between them. tar first lays every file end to end, then gzip sees the whole concatenation — so a folder of many similar small text files often shrinks a bit more as .tar.gz than as .zip. For a handful of large files the difference is small.

What about Brotli and zstd?

Newer lossless packers (Brotli, Zstandard) usually beat Deflate on text, which is why websites send Content-Encoding: br or zstd when the browser supports it. You still do not save a .zip: the browser inflates the page into memory and shows it. That on-the-wire trick is related to gzip, not to “right-click, compress folder”.

When to use which

• Sending a folder to someone on Windows or a phone: ZIP. Everyone can open it.
• A backup or source tree on Linux or macOS: tar -czf project.tar.gz project/ so permissions and empty directories survive.
• One log file: gzip app.log produces app.log.gz and deletes the original (use gzip -k to keep it). There is no folder list to maintain.
• A website: let the server negotiate gzip or Brotli. That is automatic; you do not email anyone a .gz.
• A folder of photos: neither gzip nor ZIP will shrink them much — see why zipping photos does not make them smaller and the packing lesson. Resize and re-encode first.

A few commands

# ZIP a folder (Linux, macOS, Windows with tar)
zip -r photos.zip photos/
tar -a -cf photos.zip photos/     # tar on modern Windows / bsdtar

# gzip a single file (keeps permissions on the original’s metadata, not a directory)
gzip -k report.csv                # writes report.csv.gz

# The usual Unix archive
tar -czf project.tar.gz project/

# Peek without extracting
unzip -l photos.zip
gzip -l report.csv.gz
tar -tzf project.tar.gz

Related

Lossless vs lossy compression · Why a ZIP can be larger than the originals · CRC failed / unexpected end of archive · Why zipping photos barely makes them smaller (interactive lesson) · Why zipping photos does not make them smaller · Compress many photos at once · Compress an image without uploading it · Image compressor

Questions

Published 8 November 2026.