What Is the Difference Between Quantity and Unit?

Units Versus Quantity

A Mettler balance measures the quantity of sample with precision of 0.1 mg units.
A Mettler balance measures the quantity of sample with precision of 0.1 mg units. US DEA

What is the difference between a quantity and a unit? If you are working science or math problems, the answer to this question is that quantity is the amount or numerical value, while the unit is the measurement. For example, if a sample contains 453 grams, the quantity is 453 while the unit is grams. In this instance, the quantity is always a number and the units are any measure, such as grams, liters, degrees, lumens, etc.

As another example, in a recipe, the quantity is how much you need and the unit describes what you use to measure it. Three tablespoons and 3 teaspoons have the same quantity, but they use different units. It's important to note the units, whether it's in the lab or in the kitchen!

Units in Science Versus Math

There are, however, other ways to answer the question of quantity versus unit. A quantity may be considered to be a nonspecific number of items, particularly ones that would be hard to count. You could refer to a "quantity of water" or a "quantity of air" and not cite the number of molecules or mass.

Additionally, units sometimes refer to individual sets. For example, if you are studying chemistry, you may have a unit on gases, a unit on conversions, and a unit on balancing equations. A set of rooms in an apartment building may also be called a unit. Any removable component in a piece of electronics may be called a unit as well. If the term "unit" is used this way, quantity can mean how many units you have. If you need 3 units of blood for a transfusion, the number three is the quantity, with each unit being a single container of blood.

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