Mass is a measure of how much matter a body contains. In everyday language it is often called weight, but in physics there is a distinction between mass and weight. The mass of an object does not change regardless of where it is located. It is measured in kilograms with the symbol \( \large kg \).

 

 

SI unit of mass

 

The fundamental unit of mass in the SI system is the kilogram:

 

$$ \large 1 \text{ kg} = 1000 \text{ g} $$

 

One kilogram equals the mass of 1000 grams. Smaller and larger units can be expressed using prefixes such as milli-, centi-, deca-, hecto-, and kilo-.

 

 

Derived units

 

The table shows the most commonly used mass units and their relation to the gram:

 

Factor	Name	Symbol	Unit
\( \large 0.001 \)	Milligram	mg	\( \large 1 \text{ mg} = 0.001 \text{ g} \)
\( \large 0.01 \)	Centigram	cg	\( \large 1 \text{ cg} = 0.01 \text{ g} \)
\( \large 0.1 \)	Decigram	dg	\( \large 1 \text{ dg} = 0.1 \text{ g} \)
\( \large 1 \)	Gram	g	\( \large 1 \text{ g} = 1 \text{ g} \)
\( \large 10 \)	Decagram	dag	\( \large 1 \text{ dag} = 10 \text{ g} \)
\( \large 100 \)	Hectogram	hg	\( \large 1 \text{ hg} = 100 \text{ g} \)
\( \large 1000 \)	Kilogram	kg	\( \large 1 \text{ kg} = 1000 \text{ g} \)

 

 

Examples

 

• An apple has a mass of about \( \large 0.2 \text{ kg} \).
• One litre of water has a mass of \( \large 1 \text{ kg} \).
• A person may have a mass of around \( \large 70 \text{ kg} \).