I see a fair number of questions on production ratios (on reddit) and amazingly, nothing on the wiki seems to deal with it, so here it goes. (This is really just a draft I plan on cleaning up and putting on the wiki).

The beginner says “Aha, I need a ton of <insert something here> so I’ll build some factories for it.” Then the factories sit idle most of the time. Adding factories doesn’t work if you don’t have the necessary inputs. So, how to figure that out? The easiest way is decide how many outputs per second you want.

For simple things (such as red science) you can build a lot of factories because the inputs (copper + gears) are either fast to make or basically infinite. (OK, not really, but if you aren’t smelting enough copper you have bigger problems). But let’s consider science pack 3 (blue science). Here’s the formula (as of 0.15):

1 Advanced (Red) Circuit + 1 Engine Unit + 1 Assembling Machine 1 (Grey) and 12 seconds makes 1 blue science.

(Thanks to Dave McW’s wonderful cheat sheet for this).

So, the easiest way to is to target some # of packs per second. Let’s say you want one. Picking round numbers makes it easy.

As the old saying goes ‘You can’t make a baby in one month by getting nine women pregnant.’

But you can average a baby a month that way.

To average 1 blue/second, we need 12 factories. (I’m ignoring the speed multiplier for assembling machines. It isn’t actually 12 seconds, depending on the factories. If you have all blue assembling machines (level 2) and change everything to level 3s, the number you get will speed up, but there will be no bottlenecks or slowdowns if they are all even).

Rule of thumb — If you want one unit output per second, you need as many factories as the time it takes.(Again, ignoring speed multipliers). If you want Z per second, you need Z times the number of seconds it takes one factory.

So, we need 12 factories producing blue packs. Now the reason to pick a nice round number like “one blue a second” is that we now know that we need one red circuit per second, one assembling machine per second, and one engine unit per second. We have to have enough inputs.

So, what does an Engine Unit take to make?

1 Steel + 1 Iron + 2 Pipes and 10 seconds makes an engine unit.

In order to support one blue science a second, we need 1 engine per second, which means 10 dedicated engine assemblers. Similarly, we need six red circuit assemblers. We only need half of an assembly one assembler, since it only takes 0.5 seconds. We can make these factories dedicated for this output (which may make sense for some objects) or we may have a big production area (for, say red circuits) so that any overflow can be used elsewhere.

Let’s look at a more complex example: Production Science Packs (purple)

1 Pumpjack + 1 Electric Engine Unit + 1 Electric Furnace + 14 seconds gives us 2 production science packs.

If we want one purple per second, we need seven factories dedicated to production (since they produce two each every 14 seconds). Every fourteen seconds our seven factories dump out their two purple each to give us one purple per second, and every fourteen seconds they each take in a pumpjack, electric engine and furnace.

So we only need 7 of each input per 14 seconds.

We need 1/2 of a pumpjack per second (or 1 pump jack per two seconds). Ditto the other two.

Electric Engines take an engine unit (sigh), 2x electric circuits and 15 units of lubricant and 10 seconds.

If we want a dedicated line we need five factories (for 1 every other second), which will also require 5 factories for engine units (again, one every other second). (Remember our rule, we want Z per second. Z is “one-half” and the factories take 10s, so 0.5 x 10 = 5 factories.

“It’s really easy to forget the two outputs per unit time,” he wrote looking at his current factory and suddenly realizing why there’s such a backlog of electric engine units. Ah well, I can divert some of that production and my pump jack production….In fact, there are a number of practical matters. If you only use purple science packs intermittently, you can get by with lower inputs and you’ll buffer some up while researching things that don’t require purple).

So far we’ve just spoken of production speed, but if you start getting into big numbers, you may have to worry about throughput. Maximum throughput of a yellow belt is 13.33 items per second. If you need 15 or 20 items per second, you’ll requirea faster built (or a second belt) otherwise the first factories in your line will consume all the inputs and choke off your remaining factories. For our examples, that hasn’t been a huge concern (although technically it means that our one purple per second is actually 13.33 purple per 14s, assuming we have perfectly packed yellow belts). But if we wanted to go to two per second, we’d need to upgrade our belts (red belts are exactly twice as fast). If we wanted to go to 5 a second, that would require multiple lines (or maybe having a staggered line where we produce a few intermediates, then a few purples. But that way lies madness).

You can do this to see compare if you have enough labs to consume your science production (or too many labs) although that’s tricky because the colors you need (and times) change based on what you are researching. But typically research takes 30s or 60s (some of the early game research takes less, and some military researches take 45 and braking speed takes 35!) If you produce one (of each color per science) then you can keep 30 labs working all the time, and your 61st lab is guaranteed to sit idle (assuming you never stopped), but in reality you will stop from time to time….

I haven’t done the math on launching one Rocket Per Minute, but throughput becomes a big concern. 1000 Rocket Control Units (which are required per rocket) requires just shy of 40k iron per minute, 650ish iron per second (smelting and transport). Of course those actually have a bunch of intermediate steps, but that’s 17 lanes of express belts just for iron. (In reality, its a bunch of trains to various outposts to make green circuits, etc). And rockets have a bunch of other parts.