Purple science almost made me quit Factorio. I had a smooth run through red, green, and blue -- then hit production science and watched my entire base crawl to a halt. Electric furnaces stalled because I didn't have enough steel. Productivity modules demanded more circuits than my entire green circuit line could produce. Rails backed up the iron bus. Here's the setup that actually works.
The Three Ingredients
Production science pack (purple) needs three components that each pull from different parts of your factory:
| Ingredient | Raw materials | Typical bottleneck |
|---|---|---|
| Electric furnace | Steel, red circuits, brick | Steel throughput |
| Productivity module | Red circuits, green circuits, sulfur | Red circuit bus |
| Rail | Steel, iron | Iron plates (consumes 4 iron per rail) |
None of these share a sub-factory. That means you can't just drop a few assemblers and call it done -- each ingredient needs its own mini production line.
Optimal Ratio for 5 SPM
Here's the ratio that works for a stable 5 science per minute, scaled from the established Factorio community math:
| Component | Machines | Feeds how many science assemblers |
|---|---|---|
| Purple science assemblers | 6 | Target output |
| Electric furnace assemblers | 2 | Feeds ~6 assemblers |
| Productivity module assemblers | 2 | Feeds ~6 assemblers |
| Rail assembler | 1 | Feeds ~8 assemblers |
| Engine unit (already on bus) | - | Shared from blue science supply |
The math behind these numbers:
- Each purple science assembler (clocked at 1.25 crafting speed with AM2) consumes 0.5 furnaces/sec, 0.5 modules/sec, and 1 rail/sec
- One furnace assembler produces 2 furnaces/sec = feeds 4 science assemblers
- One module assembler produces 2 modules/sec = feeds 4 science assemblers
- One rail assembler produces 2 rails/sec = feeds 2 science assemblers
I ran this all through FactorioLab after my first attempt failed. My mistake was building one assembler for each ingredient and wondering why the science line backed up.
Layout -- Compact Purple Science Cell
A compact purple science array fits in about 20x40 tiles. Here's the pattern:
Row 1 (top): Electric furnace production. Two assemblers pulling steel plates (bottom belt) and red circuits (side belt). Output electric furnaces onto a dedicated belt running toward the science line.
Row 2 (middle): Productivity module production. Two assemblers pulling red circuits, green circuits, and sulfur. Output to a belt running alongside the furnaces.
Row 3 (lower): Rail production. One assembler pulling steel and iron plates. Place this closest to your main bus since rails need the most raw material throughput.
Row 4 (bottom): Six science assemblers in a row. Each pulls from the three ingredient belts above and outputs to a single science belt below.
The science belt feeds into your existing lab line. If your lab line already handles red, green, and blue science, add this at the end.
Raw Material Budget
For 5 SPM of purple science running continuously:
| Input | Rate | Source |
|---|---|---|
| Steel plates | ~8/sec | 20 steel furnaces on iron |
| Iron plates | ~6/sec | 10 steel furnaces |
| Green circuits | ~3/sec | 1 assembler |
| Red circuits | ~1.5/sec | Shared with blue science |
| Sulfur | ~0.5/sec | Shared with blue science |
| Stone brick | ~0.5/sec | 2 furnaces |
The steel demand is the killer. 8 steel plates per second means your iron smelting column needs roughly 60 stone furnaces worth of iron production just for purple science. If your existing iron smelting is running near capacity, purple science will break it.
Where I Got Stuck
The productivity module trap. Productivity modules themselves are the ingredient, and they need sulfur. If your blue science is already consuming most of your sulfur output, purple science shuts down before it starts. Solution: build a dedicated sulfur chemical plant for purple science, separate from blue.
Bus starvation. Purple science pulls heavily from steel. Steel comes from iron plates (5:1 ratio). If your main bus has one iron belt feeding both steel production and everything else, purple science eats the entire belt and your mall stops making belts and assemblers. Solution: add a second iron plate belt to the bus before launching purple science.
Rail overconsumption. One science assembler consumes 1 rail per 5 seconds. Rails cost 1 steel + 1 iron. At 6 science assemblers, that's 1.2 rails/second = 1.2 steel + 4.8 iron/second just for rails. On yellow belts, that's a full lane of iron dedicated to rail production.
Scaling to 45 SPM
To go from 5 to 45 SPM purple science:
| Scale | Science assemblers | Furnace assemblers | Module assemblers | Rail assemblers |
|---|---|---|---|---|
| 5 SPM | 6 | 2 | 2 | 1 |
| 15 SPM | 18 | 6 | 6 | 3 |
| 30 SPM | 36 | 12 | 12 | 6 |
| 45 SPM | 54 | 18 | 18 | 9 |
Each 15-SPM block can be built as a repeatable cell. At 45 SPM, you'll need:
- 180+ steel furnaces on iron (or electric with modules)
- Dedicated iron and copper bus expansion
- 4+ belts of iron plates just for purple science
- A separate red circuit plant doubled
The steel demand at scale changes your entire base layout. At this point, outpost-based iron smelting feeding a train network beats a main bus.
Bottom Line
Purple science is the point where a main bus factory hits its first real ceiling. The three-ingredient setup forces you to think in sub-factories, and the steel demand exposes any weakness in your smelting. Build it right once and it scales cleanly; build it wrong and your entire base starves.
Numbers to remember:
- 6 science assemblers + 2 furnace + 2 module + 1 rail = 5 SPM
- Steel demand is the primary constraint
- Dedicated sulfur plant prevents starvation from blue science
- Purple science needs its own iron belt if your bus is tight
Previous: Blue Science Guide Next: Yellow Science Guide
Community Verification & Resources
- Official Factorio Wiki -- Production Science Pack -- recipe timings and crafting speed formulas
- FactorioLab Calculator -- SPM-optimized purple science builds
- Reddit -- Purple Science Layouts -- community compact designs
Related: Yellow Science Guide | Beacon Module Guide | Smelting Ratios