What do the notations PPM/PPB/PPT mean?

The terms PPM (Parts per million), PPB (Parts per Billion) and PPT (Parts per trillion) are abbreviations used to express concentration levels in liquid or solid solutions.

Their purpose is to simplify the expression of a low concentration of a parameter present in a liquid or solid solution. Like percentages representing X out of 100, these three acronyms all represent a fraction; it is just much smaller.

Although the term Parts Per Million (PPM) is more widely recognized than its counterparts PPB and PPT, they all have the same purpose; to simplify the expression and understanding of extremely low concentrations. The only difference between PPM, PPB and PPT is the concentration level.

Since we are experts in water treatment, we will only elaborate on the use of these abbreviations for liquid solutions. However, it is important to specify that the basic unit used for the calculation of PPM, PPB and PPT are similar whether we are talking about liquid or solid.

• Liquid = 1 liter or 1000 ml
• Solid = 1 kilogram or 1000 g

Therefore, although we use liquid examples, the explanations can be used to understand the same notations used for solids.

What do these notations amount to?

As mentioned above, PPM stands for "parts per million". Even if you understand what that means, it can be difficult to understand the true value of a PPM, PPB, or PPT. To put things in perspective, here is a comparison of concentration calculated against a liter of liquid.

To summarize, the PPM, PPB and PPT notations are useful to simplify communication and understanding in identifying concentrations. Imagine being told by the government that your uranium concentrations cannot exceed 0.0000005 ml per liter... that's a lot of zeros to count!

Anyway, here is a table comparing the different notations discussed in this text.