Video: How we measure substance

Hello again, I’m Doctor Bruce Warrington, Australia’s Chief Metrologist.

I’ve been talking about the base units of measurement, beginning with the second, metre and kilogram. The others are the kelvin for temperature, the candela for luminous intensity, and the ampere for electric current.

The last is the mole, which is a measure of stuff—of how many atoms or molecules you have of a particular substance, such as water, or gold, or DNA. For example, when we get our blood tested our glucose levels are measured in moles per litre.

Following an international decision last year, from 20 May 2019 the number of molecules in one mole will be 6 point 022 140 76 times ten to the power twenty-three. This number is the Avogadro constant. Even though it’s huge – twenty four digits long – a mole of water molecules is roughly a spoonful.

The mole is arguably the unit with the biggest reach, spanning all of chemistry and biology. Here at the National Measurement Institute we make an enormous range of measurements that depend on it, from levels of vitamins and pesticides in food, to the makeup of drugs and pharmaceuticals, to testing for environmental contaminants in soil, air and water.

It’s time for me to go now – I hope you have enjoyed this series on the base units of measurement, and see you in the future!