What suffix is used to describe the quantity of something?

The suffix used to describe the quantity of something is -ity.

Here are some examples:

* Quantity: the amount of something

* Capacity: the maximum amount something can hold

* Quantity: the amount of something

* Elasticity: the ability to stretch or deform

* Density: the amount of mass per unit volume

There are other suffixes that can also be used to indicate quantity, but "-ity" is the most common.