I think it works differently. It’s a bit tricky. First of all you need to understand how to calculate landscape dimensions (Landscape Technical Guide | Unreal Engine Documentation is a good resource). UE4 uses 1 unit = 1cm scale proportion. Landscape is scaled to 100x100x100 (as Kjasi mentioned).
To calculate exact size you need to do a little math: (Overall Resolution - 1) * 100 (which is X scale) by (Overall Resolution - 1) * 100 (which is Y scale)
Let’s take a very small landscape as an example:
Section size: 7x7
Sections per component: 1x1
Number of Components: 2x2
so the Overall Resolution: 15x15
(15-1)*100 = 1400 cm
1400 cm * 1400 cm = 1960000 cm^2 = 196m^2
In your case the surface area is: 16257024 m^2 = ~16,26 km^2
Correct me if I’m wrong