Question

What is the quantitative measure of inertia?

Answer 1

`kg` or kilogram. In other words: the same as mass (these are identical).

Explanation:

Inertia is often described as "unwillingness to move".

Changing the velocity or direction of movement requires Force.
The formula `vecF=mxxveca` explains that a mass (in `kg`) needs a force (in `N=kg*m//s^2`) to accelarate (in `m//s^2`).

Notice that the arrow above the letters denotes a vector, i.e. direction is important.