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 1W = 1J / 1s, ie. one Joule of work being done every second.
The game commonly deals with larger units, namely kilowatts (kW) and megawatts (MW).
Lamps use 5kW while turned on. A Radar uses 300kW while active - equivalent to 60 lamps. One Steam engine is capable of outputting 510kW.
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 represents the work being done (total energy transferred) by a power of one watt applied for one second: 1J = 1W * 1s.
In-game, Fuel is nothing than work. For example, every piece of coal burned will produce 8kJ. One Basic accumulator is capable of storing 5MJ.
It doesn't make much sense to calculate work with the (in real-world) much more common kilo Watt hours (kWh, 1 kWh = 3600 kJ), cause the game runs more or less in real-time and it is not useful to calculate that case with hours.
Time
Tick (1/60s)
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)
See also
(Missing here: Capacity, which is either the volume of something or Productive capacity)