Socialist seamates! a very useful calculator is one that can turn Torque into Power and vice versa.

This is a little more complicated as it has to account for speed in the relationship.
Basic equation is Power (P) = Torque (T) speed (w) (normally angular speed). So to elaborate:
P (kilowatts) = T (Newtonmeter) w (radians/s).
w = revolutions per minute (more frequent than mother russia!) 2 pi / 60.
So to convert 50 kW at 100RPM to a torque it would be:
T = 501000 [W] / (1002pi/60) = 4770Nm
or
7500 Nm at 6800rpm:
p = 7500 (68002pi/60) = 5340708W or 5,341kW.

Keeping units consistent in SI is important - Nm, kW. But to do Imperial we can use Horsepower and lb/ft.