SliTaz Linux is really small! As a super lightweight Linux distro, the compressed ISO form takes up about 50MB. It was mentioned in the SliTaz website that the decompressed root file system will take up 100MB. A quick check with my install, the storage used up so far was about 60MB.
Porteus is a super lightweight Linux operating system taking up about 300MB of storage space. It uses a squashed format for storing its core files, and will decompress when you boot. It also uses a modular approach whereby you install pre-compiled packages as opposed to the standard Linux using package manager.
Because it is also portable, it is easy to install into any existing Linux installation. In my case I copied the ISO files and placed it in the same partition as my FossaPup, KolibriOS, SLAX, SliTaz, TinyCore and SystemRescue.