Indium Blog

Explanation of “Nines” Regarding Metal Purity

  • Indium

  • This post involves the purity of indium and all other metals and alloys.

    Some of my favorite topics to discuss are those which seem to ‘trip up’ readers who are learning something new. After all – we have all been there: learning a new subject and having to research a term that will later become something we use every day, or having to ask for clarification of a term that someone assumes everyone already understands. I like helping people grow.

    A set of related terms used in the metals market is, “nines”. This is a simple concept: “nines” refers to the purity of a material. For instance: 99.99% indium is often described as, “Four Nines” and typically written as “4N”. All three of these terms mean the same thing, and are used interchangeably in this industry. This rule can be extended to other purities, such as 99.999% and 99.9999%. (“Five Nines” and “Six Nines” respectively).

    Another aspect of this terminology is used to describe materials that do not fully meet one of the above specifications. An example of this is as follows:

    99.995% = “Four Nines Five” or “4N5”

    99.9998% = “Five Nines Eight” or “5N8”

    99.9X% = “Three Nines Plus” or “3N+” (which is somewhere between 99.9% and 99.99%)

    I hope this explanation is helpful. If you have anything you’d like to add or ask about the topic, feel free to comment below or email me at


    Authored by previous Indium Application Manager Jim Hisert