use cb or som+som to find enemy defense.
Then, i use the following calculation
(EnDef)*1.01[oversend 1%]*1.09[4 generals, 9% bonus]/OME[offensive military efficiency]=Raw offense sent.
So if say ur offense is full elites, u can take RawOff/6 to find the number of elites sent. If u need to send horses/prisoners, subtract from RawOff then divide by elite strength.