Derived Units - with formulas

The international system of units (SI) consists of 7 fundamental units and 2 supplementary units.

And all other than these 9 units are derived from these units.

These are the seven fundamental units.

These are the two supplementary units.

But we have several physical quantities rather than these fundamental and supplementary quantities. Like area, volume, density, etc.

So, we have to derive the unit of these physical quantities (area, volume and density) from the fundamental unit.

And that unit is called derived unit.

Let’s discuss the derived units.

Derived unit is the unit which is derived from the fundamental units.

For Example, The area is defined as the product of area and width. Hence, Unit of the area in SI systems will be derived as,

Now, the volume is the product of length, width and height. Hence, SI unit of Volume will be derived as,

And the density is defined as ratio of the mass to the volume and its unit will be calculated as,

The velocity is defined as the displacement travelled per unit time.

Now, we will discuss guidelines for writing SI units.

Let’s discuss the guidelines for writing SI units.

There are several guidelines for writing SI units. We will discuss one by one.

While we writing a number having more than five digits, then it should be placed in a group of three separated values.

For example, 5689234.242356 should be written as 5 689 234.242 356.

A dash (-) is needed to be used to separate units that are multiplied together in SI units.

For example: kg m should be written as kg-m.

The plural of units are not allowed to use in the symbol of units.

For example: if units are second or seconds then we can write only .

If unit symbol is derived from any scientist name then it will be written with capital letters. Otherwise, it will be written with small letters.

For example: Newton unit comes from the name of Issac Newton. Hence it is written as .

And meter is written as .

While we are writting a unit with full name, then it should be in small letters.

For example: when we are mentioning the unit then we should write it as ‘newton’ instead of Newton.


Derived unit is the unit which is derived from the fundamental units.

For example: unit of area,

And unit of volume is derived as,

The End