I want to know how to calculate the switching loss of mosfet which is connected at the output of 1845 IC which is a Current Mode PWM Controller (Unitrode IC). There is no specific formula given in the datasheet. The LTC1778 regulator IC the formula given is

Transition Loss @ (1.7A–1) VIN^2 IOUT CRSS f.

Can  we use this formula. Or is there a different approach.