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Derived Units

Derived units are quantities that are calculated from two or more measurements. Derived quantities cannot be measured directly. They can only be obtained by combining different SI units.

Three examples of derived units are volume, density, and pressure.


Volume

Volume is the amount of space an object takes up. You are measuring volume when you answer the question "How big?"

Volume is often measured in liters (L). One liter is equal to half a two liter bottle of soda.

two liter soda bottles

Other common measurements for volume are:

  1. milliliter (mL)
  2. cubic centimeter (g/cm3)

These units are equal to each other, about the size of a sugar cube.


Density

Since matter is defined as anything that has mass and takes up space, we are able to use the mass and volume of an object to find the density of the material that makes up that matter.

Density is the mass per unit volume of a material. This formula is listed below:

Density = mass ÷ volume


Density and Derived Units

The standard SI unit of measurement for density is kg/m3 (this is read "kilograms per meter cubed" or "kilograms per cubic meter").

Another commonly used SI unit of density is g/cm3 (this is read "grams per centimeter cubed" or "grams per cubic centimeter").

1 g/cm3 is equal to 1000 kg/m3. And 1 kg/cm3 is equal to 0.001 g/cm3. See the Density Converter Calculator for help.

These are derived units since each measurement is obtained by combining different SI units.

Let's look at an example of how density is calculated. An object with a mass of 10 g and a volume of 2 cm3 would have a density of 5 g/cm3. This is calculated: 10 g รท 2 cm3 = 5 g/cm3. (Note: 1 mL is equal to 1 cm3.)

water ripples

Water has a density of 1 g/cm3 or 1 mL.


Pressure

Pressure is the amount of force exerted per unit area over which that force is distributed. The SI unit for pressure is pascal (Pa). It is also a derived unit.

person putting air in a car tire

When airing up your car tires, you must pay attention to the pressure.