Always in a physical quantity, the numerical value is inversely proportional to its units.

Hint: The numerical value along with its unit makes the measurement of a quantity. The relation between two different units for the same quantity tells us the relation between the unit and its numerical value. Using units of the measurement like kg, litre, etc, the relation between the numerical value and its unit can be found out easily.

Complete answer:
It is better to know the definitions of the terms that we are going to use in further explanation. The definitions of measurement and the unit are as follows.

The measurement is the assignment of the number to the characteristics of the materials, objects, events, etc. The physical quantities are measured with respect to a fixed quantity called the unit.

Consider, for example, x represents the magnitude and y represents the unit. Thus, the overall expression is represented as follows.
$xy = $constant
Let,
${n_1}$ is the magnitude of any physical quantity in unit system ${u_1}$
${n_2}$ is the magnitude of the same physical quantity in the unit system ${u_2}$.

So, from the units’ conversion formula of physical quantity,
${n_1}{u_1} = {n_2}{u_2}$
$ \Rightarrow \dfrac{{{n_1}}}{{{n_2}}} = \dfrac{{{u_2}}}{{{u_1}}}$

So, we can say that $n \propto \dfrac{1}{u}$. Thus, the magnitude of the physical quantity is inversely proportional to the unit of physical quantity.

Note: We can say that, for a larger numerical value, the unit associated will be smaller and vice - versa. Some of the physical quantities do not have units, as they are the ratios of the physical quantities having the same units. For example, the strain is a unitless quantity, as it is a ratio of original to the extended length, and as the length of both is same, thus, the unit gets cancelled.