How is the Factorio a embly line ratios worked out?

Factorio

Assembly Line Ratios

Get Factorio ratios right and a line runs non-stop; get them wrong and it starves half the time — and the maths gets fiddly fast.

Assembly Line Optimizer

Recipe

Target Output (items/sec)

Assembler Tier

Prod Modules

Assemblers Needed

Input Materials Req/Sec

iron plate4.00/s

How the numbers are worked out

Each recipe has a crafting time and a set of inputs, and each tier of assembler has its own speed multiplier. The calculator tells you how many assemblers of a given tier you need to hit an output rate, and how much input that asks for further up the chain.

The formula

effective speed = assembler speed × (1 − 0.05 × productivity modules)
items per craft = recipe output × (1 + 0.04 × productivity modules)
assemblers = ceil((target rate × craft time) ÷ (items per craft × effective speed))

Common mistakes

Belts are usually the first wall you hit. A ratio can be perfectly correct and still stall because the belt feeding it cannot move enough items per second, so compare the belt tier with the input rate before you build the whole row.

A worked example

One advanced circuit per second takes 6 seconds of crafting each, so assembling machine 2s at speed 0.75 need 6 ÷ 0.75 = 8 machines, fed 2 electronic circuits, 2 plastic bars and 4 copper cables a second. Put two productivity modules in each and the picture changes: each machine slows to 0.675 but yields 1.08 circuits per craft, so you need 9 machines instead of 8, while the inputs drop by about 7%.

Productivity is a trade, not a bonus

That is the general rule the calculator makes visible: productivity modules cost machine time and power to save raw materials. They pay off on expensive recipes high in the chain, where each saved input represents a lot of mining and smelting, and rarely on cheap ones near the start.

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