Factorio Forums

Hey all, this is gonna be a bit long
I've ran into a weird in-game item-per-second calculation when using productivity modules on a coal liquefication recipe (and others)

Usually, when calculating items-per-second with modules, the formula is something like
new item/s=(OG item/s)*(1+ speed)*(1+prod)
so taking +30% prod with +20% speed on gear wheel recipe for example, will get 2 * 1.3 * 1.2 = 3.12 gears-per-second
The game shows you this number when hovering over the machine

Now, here's where the problem starts: when calculating the same on ANY recipe that inputs and outputs the same resource (coal liquefaction, Kovarex enrichment...), I've figured out after much headache, that for coal liquefaction - specifically heavy oil, heavy oil/s is calculated as
heavy/s =18*(1+speed)*(1+(18-5)/18 * prod)
or more generally, prod calculation seems to be
output item/s = (OG output item/s)*(1+speed)*(1+((OG output item/s)-(OG input item/s))/(OG output item/s) * prod)

18 is the OG output heavy/s, 5 is the OG input heavy/s, making 13/18 be (what I assume is) the %net gain of heavy
Here's where I'm failing to understand - why doesn't it use the standard formula?
it seems to me that the game assumes that 5/18 will go back to the input, so I checked if the machine somehow puts some heavy back into itself when prod is used - no it doesn't.
Now i'm trying to figure out if the game shows that net output after I redirect the input back (in which case, the formula seems wrong to me, as I can just use the standard one and remove from it the input count), or that the game shows the actual output, without assuming I redirect input

All I'm trying to do is make a (custom) liquefaction station, and trying to figure out how many machines do I need to put to achieve my wanted output (and kinda trying to compare it to my non-moduled advanced oil cracking station)
though effectively this would probably change nothing what so ever ('cause there is no kill like overkill), my OCD brain can't let this go

I'm not even sure this is a bug or intended (I tend towards intended)


If anyone knows about this, and could please explain it to me the reasoning here, I'd really appreciate it.
TL;DR recipes with a resource both in input and output have a productivity calculation that strange and I can't figure out why

Part of the input is marked as a catalyst. Catalysts are subtracted from bonus production.

Yes, in other words the 25 input oil is just passed through to the output, and 65 oil is actually produced and it's only this part for which productivity applies. This is the same for all catalytic recipes in the game (though mods could specify different ratios I think).

Is there any way in-game to tell when something is marked as a catalyst? This isn't automatic. Bacteria cultivation, for example, is not a catalytic recipe.

AFAIK, the only method is to do math with the production rates with productivity present.

Not in the game I think (at least without mods), but you can look at the recipe.lua files, where ingredients listed with "ignored_by_productivity" are catalysts. However bacteria cultivation is really the only exception here.

Hurkyl wrote: Fri Sep 19, 2025 9:07 pm Is there any way in-game to tell when something is marked as a catalyst? This isn't automatic. Bacteria cultivation, for example, is not a catalytic recipe.

AFAIK, the only method is to do math with the production rates with productivity present.

Per https://factorio.com/blog/post/fff-256, catalysts are automatically calculated unless manually overridden. I think the automatic rule is that if it's in both the input and output, it's a catalyst. AFAIK the only base game catalytic recipes are coal liquefaction and kovarex enrichment.

computeraddict wrote: Fri Sep 19, 2025 10:17 pmPer https://factorio.com/blog/post/fff-256, catalysts are automatically calculated unless manually overridden. I think the automatic rule is that if it's in both the input and output, it's a catalyst. AFAIK the only base game catalytic recipes are coal liquefaction and kovarex enrichment.

This FFF (from 7+ years ago!) is no longer correct; catalyst_amount has been replaced by ignored_by_productivity value in Recipes' Product specifications. It is indeed only used by a few recipes in the game:

• Coal Liquefaction
• Kovarex Enrichment
• Pentapod egg & Fish breeding
• Cryogenic science pack / Quantum Processor production (Fluoroketone component)

It has been stated on the Forums that Bacteria Reproduction is intentionally not catalytic.

Good Luck!