Scaling asymmetric object (math)

already figured it out by myself.

Scaling works according to what the pivot point is set at.
Apply scale (ctrl+A in object mode), might as well apply rotation as well.

You objects scale will now be “1”, pressing S to scale in object mode and then typing 1.2 will scale the object 20% larger.
The object scales from the pivot point, it is a good idea to have the origin at the base of the object and set as the pivot point to make scaling more predictable.