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 the 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. For this example, the quantity is always a number, while units are any measure, such as grams, liters, degrees, lumens, etc. In a recipe, the quantity is how much you need and the unit describes what you use to measure it. For example, 3 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. A quantity may also 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.

Units sometimes refer to individual sets. For example, if you are studying chemistry, you might have a unit on gases, a unit on conversions, and a unit on balancing equations. A set of rooms in an apartment building may be called a unit. Any removable component in a piece of electronics might e called a unit. 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 3 is the quantity. Each unit is a single container of blood.

More About Units and Measurement