A main bus is the layout most Factorio players adopt once red and green science run on their own: the plates and intermediates that many recipes share run down a set of parallel belts in the middle of the base, and every production line takes what it needs off one side. It replaces "where does this belt come from?" with a rule you can extend for the rest of the game.
This guide is written for Factorio 2.0 (base game). Numbers are for normal-quality items and come from the official Factorio Wiki. Space Age is mentioned only where it changes something. If you are still in the first hour, start with the Beginner Guide — a bus is not where you begin.
How to set up a main bus
| Order | Item on the bus | Belts to plan | When it joins |
|---|---|---|---|
| 1 | Iron plate | 4 (one full group) | From the start of the bus |
| 2 | Copper plate | 4 (one full group) | From the start of the bus |
| 3 | Electronic circuit (green) | 1–2 | As soon as green science runs |
| 4 | Steel plate | 1 | After Steel processing |
| 5 | Stone brick (optional) | 1, or one lane | For walls and electric furnaces (purple science) |
| 6 | Plastic bar | 1 | After oil processing |
| 7 | Advanced circuit (red) | 1 | For blue science and modules |
| 8 | Sulfur | One lane is often enough | For blue science and sulfuric acid |
| 9 | Battery | One lane | For utility science and robots |
| 10 | Processing unit (blue) | 1 | For utility science and the rocket |
The layout rules that go with the table:
- Groups of 4 belts, 2 empty tiles between groups. A basic underground belt reaches 4 tiles, so it can pass under one full group and surface in the gap. The official wiki tutorial recommends this exact spacing.
- Reserve the slots before you need them. Leave empty belt positions for plastic, advanced circuits and the rest. Inserting a new belt into the middle of a running bus later means rebuilding every take-off downstream.
- Production on one side only. Take-offs leave the bus on one side; the other side stays free so the bus can grow wider.
- Take items off with an underground belt or a splitter, both unlocked by the Logistics research (20 red packs). A splitter shares a belt 1:1; an underground belt lets the take-off pass under the belts between it and the production line.
- Leave room between production blocks. The wiki tutorial suggests at least 3 tiles, ideally 6 to 10, so each block can grow without hitting the next.
You do not need all 4 iron belts on day one. Lay the first one or two, leave the other positions empty and fill them as smelting grows. What you should not do is start with iron and copper side by side and no gap — that is the bus everyone ends up tearing down.
Why a main bus, and its honest downsides
A bus solves the mid-game problem: dozens of recipes need the same few materials, and running a dedicated belt from smelting to each new line turns into spaghetti. With a bus, every new product follows the same pattern — find the next free spot along the bus, take off what it needs, build. The factory stays readable, which matters more than efficiency when you are learning.
The costs are real, and the wiki tutorial lists most of them:
| Layout | Strength | Weakness |
|---|---|---|
| Main bus | Easy to read and extend; works with belts only | Uses many belts and much space; fixed throughput ceiling; items sit on belts as buffer |
| Direct belts (spaghetti) | Fast to build early, no wasted belts | Hard to extend; every new line means rerouting |
| City blocks with trains | Scales far beyond any bus; blocks are independent | Needs trains, stations and blueprints before it pays off |
| Logistic robots | No belts for low-volume items; very flexible | Late unlock; poor for high-volume plates over distance |
The weakness that bites hardest is what the wiki calls a fake bus: belts that look like a supply line but are not saturated. Eight belts of iron fed by smelting that only fills three deliver three belts' worth, and the lines at the end of the bus starve while the start looks fine. A bus is only as wide as the smelting behind it.
Belt throughput
Every belt has two lanes and holds the same density at every tier; only the speed changes. These are the official figures:
| Belt | Items/s (both lanes) | Per lane | Underground reach | Research |
|---|---|---|---|---|
| Transport belt (yellow) | 15 | 7.5 | 4 tiles | Available from the start; undergrounds and splitters need Logistics |
| Fast transport belt (red) | 30 | 15 | 6 tiles | Logistics 2 (red + green) |
| Express transport belt (blue) | 45 | 22.5 | 8 tiles | Logistics 3 (red, green, blue, purple); needs 20 lubricant per belt |
| Turbo transport belt | 60 | 30 | Not covered here | Space Age only; needs tungsten from Vulcanus |
Two consequences for the bus. First, upgrading yellow to red doubles the bus without making it wider, so a 4-belt iron group goes from 60 to 120 plates/s. Second, the 4-belt group comes from the yellow underground's 4-tile reach. Red and blue undergrounds reach further, but keep the groups at 4 anyway: a single leftover yellow underground in a take-off would otherwise fail to cross.
How many belts for a science target
Bus sizing guides often give belt counts with no source. A more honest way is to count plates per science pack. The totals below are the wiki's "total raw" figures, and the per-second numbers are simple arithmetic on them.
| Science pack | Iron plate per pack | Copper plate per pack | Other bus items per pack |
|---|---|---|---|
| Automation (red) | 2 | 1 | — |
| Logistic (green) | 5.5 | 1.5 | — |
| Chemical (blue) | 12 | 7.5 | Plastic and sulfur (see below) |
| Production (purple) | 52.5 | 19.2 | 11.7 stone; plastic via circuits |
The iron figures already include the iron turned into steel and gears. A blue pack, for example, comes from a recipe of 3 advanced circuits, 2 engine units and 1 sulfur for 2 packs, so each pack also needs 3 plastic bars (2 per advanced circuit) and 0.5 sulfur.
Steel is the hidden cost of purple science: per 3 packs, the electric furnace takes 10 steel plates and the 30 rails another 15, so 45 SPM of purple alone uses over 6 steel plates per second.
What that means in belts, with SPM meaning packs per minute of each colour:
| Target | Iron plate/s | Copper plate/s | Roughly |
|---|---|---|---|
| 60 SPM red + green | 7.5 | 2.5 | Half a yellow belt of iron |
| 45 SPM red + green + blue | 14.6 | 7.5 | One yellow belt of iron, half a belt of copper |
| 90 SPM red + green + blue | 29.3 | 15 | Two yellow (one red) belts of iron, one yellow of copper |
| Add 45 SPM purple | +39.4 | +14.4 | Close to three more yellow belts of iron |
The lesson is in the last row. Red, green and blue science are cheap; purple and yellow are what turn a comfortable bus into a cramped one. If you are aiming for the rocket at a moderate rate, plan the full group of 4 iron belts and upgrade them to red before you start purple science. The figures assume no productivity modules; with them, you need less.
Take-offs that do not starve the end of the bus
A take-off is any point where items leave the bus for a production line. Three designs cover almost everything:
-
1
Splitter take-off
Put a splitter on the bus belt. One output continues down the bus, the other turns toward the production line. Without priority, the splitter shares items 1:1 until the production side backs up, then sends everything onward. With output priority set to the take-off side, the production line gets a full belt first and only the excess continues.
-
2
Underground crossing
When the item sits on a belt that is not the outermost one, the take-off belt goes underground to pass beneath the belts between it and the production side, then surfaces in the 2-tile gap or beyond the bus. This is why the gaps matter.
-
3
Single-lane take-off
Most lines need far less than a full belt. Side-loading a belt onto another puts all its items on one lane, and the wiki notes that the tunnel half of an underground belt blocks items coming from the side. Using these, you can take only one lane, which halves the most the take-off can draw.
After a take-off, the bus belt it pulled from is lighter than its neighbours. If the next few lines all pull from the same belt, that belt empties while the others stay full and back up — a fake bus within the bus. The fix is cheap: after a take-off, place splitters between that belt and its neighbour so items shift across, which is what the wiki tutorial calls inline lane balancing. Always take off from the outermost belt of a group, so the shift only ever runs in one direction.
The end of the bus always starves first. Every take-off upstream gets first pick. If total demand exceeds supply, the newest line at the end runs short no matter how cleverly the bus is balanced. When that happens, add smelting at the start of the bus — not balancers in the middle.
When you need balancers, and when you do not
A balancer spreads items evenly over several belts, built from splitters that each share 1:1. The wiki is clear that many designs have internal bottlenecks, so a balancer is only worth building when the flow is genuinely uneven.
| Situation | Balancer? | Why |
|---|---|---|
| Belts on the bus that are backed up at the start | No | Every belt is already full; there is nothing to even out |
| Several smelter columns merging into the bus | Sometimes | Uneven columns leave one bus belt short; a balancer, or simply more furnaces on the short column, fixes it |
| After a take-off | No full balancer | A splitter between neighbouring belts shifts items across |
| Unloading trains onto belts | Yes | Wagons empty unevenly, and a balancer keeps every output belt fed |
What not to put on the bus
- Copper cable. The wiki uses it as the example: cable takes more belt space than the copper plates it comes from. Make it next to the circuit assemblers that use it.
- Iron gear wheels — optional. The wiki lists them as a common bus item because a gear packs two iron plates into one slot. Many players still make them on site, since most gear users sit next to an iron belt anyway. Either works; just do not run both a gear belt and the iron to make gears in the same place.
- Single-use intermediates. Engine units, pipes and similar items with one or two consumers belong next to those consumers.
- More than two items on one belt. The wiki recommends at most two different items per belt, one per lane. A lane of sulfur next to a lane of plastic works; three or four items on one belt jam.
- Fluids, unless you want them. Sulfuric acid, water and lubricant can run alongside the bus in pipes. The wiki calls them optional; many players make them where they are used.
Factorio 2.0 changes that matter for a bus
Most 2.0 changes leave the bus pattern alone, but a few are worth knowing:
- Smart dragging of underground belts. 2.0 added smart dragging for underground belts and pipes, and smart belt building now also places an underground when you build over a belt gap with belts on both sides. Crossing the bus by hand is much less fiddly.
- No rocket control unit. The rocket part now uses a processing unit, a low density structure and rocket fuel; 100 parts per rocket in the base game. Older bus guides that reserve a belt for rocket control units are out of date.
- All inserters can filter. Filter inserters were removed and every inserter can use filters, which helps when you take one item off a mixed belt.
- Circuit connections. A belt connected to the circuit network can read the whole belt segment, and splitters can connect to the circuit network in later 2.0 versions. Both make it easier to watch whether the bus is really full.
- Space Age only: turbo belts (60/s), and stack inserters that place stacked items on a belt and raise its throughput. Neither applies to a base-game bus.
Scaling beyond the bus: when to move to trains
A bus has a hard ceiling: belts per group, times belt speed. When the bus would need more than a few blue belts of a single plate, or when your ore fields are far enough away that you already bring plates in by train, the bus has stopped being the simple option.
Railway is unlocked with red and green science (prerequisites: Engine and Logistics 2), so trains are available well before the rocket. A common path is:
- Build a bus for the first rocket. It is the fastest way to learn every production chain.
- Feed the start of the bus by train once local ore runs low. The bus stays, the smelting moves.
- For a larger base, switch to city blocks: separate blocks connected by rail, each producing one thing and served by train stations.
For the science order behind all this, see the Progression Guide. A larger base also pollutes more, so read the Defense and Pollution Guide before you double your smelting.
Common mistakes
- No gaps between groups. Without the 2-tile gap, take-offs cannot cross, and the bus has to be rebuilt.
- Starting the bus too early. Before green science runs, a small direct layout is faster. The Beginner Guide covers when to start.
- A fake bus. Laying 8 iron belts behind smelting that fills 3. Count furnaces, not belts.
- Pulling everything from one belt. Take off from the outer belt and shift items across with a splitter afterwards.
- No reserved slots. Plastic and advanced circuits arrive later, and there is no room for them.
- Building on both sides. It blocks the bus from getting wider and forces take-offs to cross each other.
- Copper cable on the bus. It costs more belt space than the plates it is made from.
★Honest Take: the best layout for learning, not the best layout
The main bus is the right layout for a first rocket. It is not the most efficient one — it uses more belts, more space and more buffered items than a direct design — but its value is that it keeps a growing factory understandable. Every new line follows the same pattern, so you spend your attention on production chains instead of on untangling belts.
Where it falls short is scale. The plate counts above show why: red, green and blue science fit comfortably on a modest bus, and purple and yellow do not. Players who stick with one bus far past the rocket end up widening, upgrading and rebuilding it. Use the bus to learn the game and reach the rocket, then move to trains without regret.
