Militia Cost
The answer
Formula
A 36-man regiment ≈ 18 tier-3 plots; 1 iron slab → 1 spear (flowchart 0.8.065+).
Militia in Manor Lords is cheap to raise and expensive to lose. Every man in the line is a family member who was also doing a job, so a battle won badly costs you next year's harvest as surely as a drought would. This calculator prices a regiment in the three currencies that actually constrain it: iron, housing and gold.
Iron is the cheap constraint
The spear chain is about as short as it gets: one iron ore becomes one slab becomes one spear. That single ratio is why a 100-iron deposit in your starting region is worth 100 armed men, and why the first thing to do on any map with visible iron is mine it.
Spears are the entry point for a reason. A spear militia held in a defensive stance, standing still and facing the charge, clears raiders and bandit camps with no losses at all. Hold the line until every attacker has committed, then flip to aggressive. Done properly you take no casualties, not merely few.
Housing is the expensive constraint
Armour, not weapons, decides close fights, and housing tier gates armour. Tier-1 plots supply helmets, tier-2 adds gambesons, tier-3 adds chainmail. A fully mailed 36-man regiment needs roughly 18 tier-3 burgage plots standing behind it.
Eighteen tier-3 plots is what makes militia a long-term project instead of a purchase. It means food variety, market supply, fuel and approval all solved first, which is why the food and farming work on this site is also military work. The calculator reports the plot count so the housing cost sits next to the iron cost, where it belongs.
Buying instead of making
The tool also prices the regiment as an import, at roughly 10g a spear. Occasionally that is right: a contested region on a short timer, or a map with no iron at all. Treat it as a one-off purchase, not a policy. Weapons bought are gold not spent on mercenaries, and mercenaries are usually the better emergency.
Two structural rules worth knowing before you build anything
Create all six militia groups before you build your first manor house. The manor's retinue otherwise consumes one of the slots, and you cannot get it back. Doing it early costs nothing, and forgetting it cannot be undone.
Hire the dangerous mercenary companies before contesting a region, not after. If you do not take them off the board, the AI will, and you may end up facing the company you were saving your treasury to hire. Pause at the start of each month to check who is available.
One tactical note that costs battles more often than it should: archers will not fire through an ally locked in melee. A ranged line behind an engaged spear wall is a line contributing nothing.
How many regiments, and where
Spread rather than concentration is the usual right answer once you hold more than one region. Plan on roughly three regiments in your home region and one to two per expansion region. Enough that a raid anywhere is met by something, without any single settlement stripping its own workforce.
Garrison an expansion region immediately. Reinforcing from home when trouble arrives is too slow: losing a defensive battle gets the settlement looted and burned even if you keep the region afterwards. And a region that loses its whole population is gone for the rest of the campaign. There is no rebuilding it. A standing garrison is cheap insurance against an outcome that has no recovery path.
One free head start worth remembering: reaching your first town level can grant a shipment of spears and large shields outright, which is a regiment's worth of equipment for no iron at all.
