Concentration

Concentration is measured in units of Molarity, Molality, or Normality.

Concentration can also be given in units of % (volume:volume), (gram:volume) or (gram:gram).

Sometimes concentration is expressed in parts per million (ppm), parts per billion (ppb) or parts per trillion (ppt).

Concentration can be measured with great precision using analytical instrumentation.  To give you an example:

        To measure parts per million (ppm) is equivalent to measuring 1 inch in 16 miles.

      To measure parts per billion (ppb) is equivalent to measuring 1 inch in 16,000 miles

        To measure parts per trillion (ppt) is equivalent to 1 second in 32,000 years.