Sometimes, the troops raised by a lord are not enough - and so he must call upon his vassals to provide more troops for a fight. Doing so taxes the loyalty of a lord's vassals but increases the number of troops he has - and it also decreases the productivity of his lands, both from reduced hands in the field and from the extra infrastructure and support required for more forces.
Increasing conscription occurs by a percentage of income on a one-for-one basis, with every 1% of your income you sacrifice leading to a 1% increase in the number of troops you can support. These troops are divided along the ordinary lines - so approximately 50% of new troops are militia, 37.5% are armsmen, 10% are riflemen and 2.5% are elites. Those percentages (and the total) are affected by government type as usual. Increased conscription also leads to a decrease in the Loyalty of your vassals; for every percent of your income you devote towards increased conscription, Loyalty and Popularity each decrease by one-half percent.
Step 1: Determine Notional Force
While individual house militaries vary in composition, the 'notional force' of a faction is based off its government type and population size. With those in hand, the notional force can be derived. The total size of that military is equal to 3%bof the total fief population, modified up or down by government type. Half of those soldiers are militia, while the other half is divided according to the values indicated by the fief's government type.
SOUTHERN REACHES (pop. 175,000) Militia 2625 Armsmen 1969 Riflemen 525 Elites 131 Total Notional Force 5250
Step 2: Determine "Mixed Percent Unit"
Every percent of conscription raises a force equal to one percent of the total strength under arms if a mixed force is being raised - and thus that 'percent unit' is important to determining the number of soldiers being raised.
SOUTHERN REACHES MIXED PERCENT UNIT Militia 26 Armsmen 20 Riflemen 5 Elites 1
Step 3: Determine "Single Percent Units"
If conscription is instead being used to raise a single troop type, the amount raised is three times the amount of single soldiers in question.
SOUTHERN REACHES SINGLE PERCENT UNITS Militia 77 Armsmen 60 Riflemen 15 Elites 3
Step 4: Calculate Conscription
If conscription is a pure levy, then multiply the percentage of conscription by the mixed percent unit and add that many new soldiers to the fief forces. (Remember that forces are paid as they train/ship.)
If the conscription is to support only a single unit type, multiply the percentage spent on conscription by the single percent unit number and add that many new soldiers. If, instead, the conscription raises multiple forces (but not in the 'standard ratios') calculate them as if they are separate single-type units.
Also note that conscription is a trickle-down affair - if a liege lord raises conscription, conscription is also raised on all of his vassals.