Units
The following units are important in Factorio.
Not all game elements are simulated physical correctly (for example the weight of items, currently no entity has a weight, the weight is measured in how many items can fetch into one stack), but those on this pages are!
Power
Power is defined as work being done per unit of time.
Watt (W)
The basic unit of power is 1 watt (W), which is defined as 1 W = 1 J/s , ie. one Joule of work being done every second.
The game commonly deals with larger units, namely kilowatts (kW) and megawatts (MW).
Lamps use 5 kW while turned on. A Radar uses 300 kW while active - equivalent to 60 lamps. One Steam engine is capable of outputting 900 kW.
Work
Work is defined as a transfer of energy, or as energy being "spent".
Joule (J)
The basic unit of work is 1 joule (J), and is equivalent to the work done (total energy transferred) by one watt applied for one second: 1 J = 1 W s.
In-game, Fuel is really just potential energy, which, when applied, does work. For example, every piece of coal burned will produce 8 MJ. One Accumulator is capable of storing 5 MJ.
It doesn't make much sense to calculate work with the much more common (at least, common in the real world) unit of kilowatt hours, because although the game runs more or less in real-time and the units are meant to be relatively realistic, 1 kW h is a lot of energy, and in fact so much so that you can't reasonably represent the value of a piece of coal that way.
Time
Tick (1/60 s)
A 1/60 second in game. This is the shortest time fraction, the game handles.
Second (s)
One second in-game. This is not guaranteed to correspond to one real second. For example, slow computers may not manage to calculate an entire tick during the corresponding real time frame of 1/60th of a second.
Day
A day has 25000 Game-ticks or 416.66 game-seconds (= 6.94 Game-minutes).
Distance / Space
Tile
The Tile is both used as a unit of distance/length and a unit of area. For example, the size of an object may be expressed as "2x2 tiles", which means the object covers an area of 4 square tiles or tiles². The unit of square tiles is often simplified into Tiles. It can be assumed, that a tile has the length of 1 meter.
Chunk
A Chunk is a quadratic area where one side is 32 tiles long. (1024 square tiles)
Logistics
Throughput
Items per time, or fluid-units per time. A unit measurement is
items / game-minute
... on Belts
Throughput = speed * density
See Transport belts.
For comparison: A Transport belt transports normally about 700 items per game-minute. A Fast transport belt up to 1200 items/min and Express transport belt nearly 1800 items / min. See physic of transport belts for more information.
... for logistic robots
Throughput depends on the distance, the number of robots and their item-stacksize. Let's assume a robot can travel 1 tile per second and can transport only one item at once. It needs also to return. Then this robot can transport 1/2 item per second. If you use 2 you can transport 1 item per second. If you double the distance, we are again at 1/2 item per second.
... for train
(Unfinished. Needs to consider also the loading and unloading time, needs to consider maximum speed...)
Capacity
Basically items per transport-unit. This depends in many cases on the item-type you use. A Cargo wagon has a capacity for 1000 items for ore, or 2000 for steel- or copper-plates.
... in stacks
A Cargo wagon has for example 20 stacks. The capacity of the wagon is 20 stacks. But the capacity of a stack depends on, what type of item you put into, so when stacks come into play, you need to say "Capacity of 20 stack iron-ore".
Density
Is measured in items per tile.
An item, that lays on ground has the size of 0.28 tiles². On one tile we can place 12.752041 items, which means, that we can put in the best case 12 items on one tile. See also physic of transport belts for more information.
... for Belts
For belts this is the same: We have two lanes on a belt, 3.571 items per lane or 7.143 item on one belt.
On belts there comes also another thing into play: Compression. Good compression is, when you fill a belt so, that you come to the maximum density and so to the maximum throughput.
... for stacks/chests
On the first glance, it is simple: A chest has the size of one tile. You have X number of stack in a chest, where you can put Y numbers of items into each, so the density is simply X * Y.
The thing changes, if you use mods, that add chest-like transport boxes, which enables to pack/box items.
See also
(Missing here: Capacity, which is either the volume of something or Productive capacity; Load, which is a measurement about the tightest bottleneck (waiting or running items))