I don't know exactly how much it will increase an oil's cSt @100* C (dependent on how much oil in sump anyway).
But I CAN tell you that it is way less viscous than; STP Oil Treatment, the Lucas c**p, or especially the old VSOT (Valvoline Synthetic Oil Treatment).
It would take a really small sump volume (like less than 3 quarts or so) to have this stuff make any impact on overall viscosity.