This link is very useful
http://www.codegrrrl.com/imperia/index.php?a=calc_military but it does not seem to have accurate numbers for the current Realm 25.
Figure 6.75 NW points for every 100 spearmen or archers you hire
13.5 NW points for every 100 swords hired
27 NW points for every 100 light cavalry
675 NW points for every 100 battering rams
NW points do round up
Remember that every time you add points, you fall into the reach of a new group of attackers who are 2 to 3 times more powerful and lose some targets who were on the edge of your 2x to 3x range.
