Countable Units — Definition & Examples

Certain metric units, some of which are commonly used in chemistry tend to not use prefixes and measure quantities (thus the term "countable units").

The candela, measuring luminous intensity is an example of a countable unit. A dozen, defined as twelve, and the half dozen, defined as six, are not traditional metric units but are common terms used colloquially by chemists. The mole (abbreviated mol), is commonly used in chemistry as it measures atomic quantity. Countable units, by virtue of not being modified by prefixes, often require no conversion.

Countable units are very much like what they sound like. They are discrete, countable objects. For example, let's say we have some apples. The countable object or unit is "apples," and our magnitude is however many apples we have.

In chemistry we often use moles (abbreviated as mol) as our unit base. Think of this in the same way that you may count shoes in pairs. If you have 5 pairs of shoes, there are 10 shoes overall. In this example the unit base is 2.

1 mole is exactly equal to Avogadro's Number, $N_{A}\approx 6.022\cdot 10^{23}$. Throwing this back to our shoe example, if we have 2 moles of shoes, then we have about $12\cdot 10^{23}$ shoes.

(Video) Units of Measurement

by Ben's Chem Videos

In this video, Ben teaches you about countable units, what they measure, and how they were created.