Production: how it works

All numbers on this page are resolved at build time from the game's own common/defines/00_defines.lua — they cannot go stale.

What one factory is worth

A production line turns factory-days into equipment. Each day the line produces

{output}_{IC} = factories \times SPEED \times \frac{efficiency}{100} \times (1 + modifiers)

in industrial capacity, which is divided by the equipment's unit cost to get items built. Base SPEED per factory per day: military 3.5, civilian construction 4, naval dockyard 2. A powered factory (see the energy section below) runs at 4.5 / 5 / 2.5 instead.

One military line accepts up to 150 factories (the UI only draws 15 slots but keeps counting past them); a construction project takes at most 15 civilian factories.

The efficiency curve

Efficiency is tracked per factory slot on the line. A new slot starts at 10% and grows toward the cap — base 50%, raised by industry technologies and some national spirits. With current efficiency $e$ and cap $c$ (both in percent), each day adds

Δ e = 1 \times 0.1 \times \frac{c^{2}}{100 e} \times (1 + growth bonuses)

percentage points. Growth is fast while $e$ is low and crawls near the cap. Integrating the daily rule gives the curve's shape:

e (t) \approx \sqrt{e_{0}^{2} + \frac{c^{2} t}{500}}

a square root in time — with a surprising consequence. A fresh line needs about 480 days to reach the base 50% cap, and raising the cap barely changes the time to reach it (a 100% cap still takes about 495 days). Cap bonuses move where the curve tops out, not how long the climb takes.

Switching production keeps only part of it

Retooling a line keeps a fraction of its efficiency (never dropping below the 10% starting floor):

Switch to	Efficiency kept
Another variant of the same equipment	90%
Equipment in the same family	70%
A parent or child of the current equipment	30%
Merely the same archetype	20%

Upgrading to the next variant of the same tank costs a tenth of your climb; retooling across archetypes costs four-fifths of it.

Idle slots bleed

A slot with no factory assigned loses 1% efficiency per day. Pulling factories off a line and re-adding them later means re-climbing the curve, so prefer steady assignments over shuffling.

Resource shortages

A piece of equipment can depend on up to 3 strategic resources, and every missing unit applies a -0.05 output penalty (a 5% hit each) to the line. The in-game progress bar turns red once the total penalty passes 0.8.

Energy: the cheapest output multiplier

A country generates 10 energy on its own, plus 9 per unit of coal. Each factory consumes 0.25 energy at base; the per-factory cost rises with your total factory count (factor 0.0225) and is capped at 6.6. A powered military factory produces 4.5 IC/day against 3.5 unpowered — about +29% output just for keeping the grid fed.

Getting the most out of your factories — checklist

Start lines early and leave them alone — the square-root curve means the first months are the cheapest efficiency you will ever buy.
Upgrade within the family — variant-to-variant switches keep 90% of your efficiency; cross-archetype retools keep 20%.
Keep every slot manned — idle slots decay 1%/day.
Fix shortages before adding factories — a -0.05 penalty per missing resource unit outweighs another low-efficiency slot.
Power the grid — powered speeds beat base speeds on every factory type (see the energy section above).