As others have mentioned, the unit scale ratio is already 1:1 between Blender and UE4.
1 Blender Unit = 1 centimeter = 1 Unreal Unit
The problem is with what we call “normal” in Blender. To be more specific, the default scale of the scene in Blender is not comparable to the scale of the scene in UE4. This is where the ratio is not equal.
Considering that the default cube in Blender is really only 2cm^3, that means the viewport is zoomed in by 100 if we compare it with UE4 standards.
One method to remedy this is to adjust the scale of the scene, as described on the Static Mesh from Blender wiki page. A few caveats regarding this method is that certain objects added in will not be to-scale with the new scale of the scene (such as cameras, empties, armatures, etc.). This method also causes possibly insignificant graphical inconsistencies in the way objects are displayed in the viewport.
To make a point, this isn’t one of the strongest features of Blender, and it’s clear that there wasn’t a large amount of foresight involved when planning it (not to discredit the developers). There are several methods out there for getting proper scale from Blender to UE4, and they all seem to have their own downsides, which honestly is not ideal for a production workflow in the least bit. If you want to find the “best” method, then I recommend trying out each one in different scenarios to find one that works best for that given scenario.