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Distinguish capacity from actual delivery
The published belt maximum assumes an uninterrupted, fully compressed two-lane belt. It is not a promise that a miner, inserter, splitter or machine will supply or consume that amount. Count rates in game-seconds, not wall-clock seconds when simulation speed is below normal.
A machine can wait for material even while the opposite lane looks full. Conversely, a line packed behind an output may indicate the receiving side is blocked, not that the belt needs more speed. The two-lane numbers below are simple upper bounds for unstacked items, not guaranteed measured throughput.
| Observed at a short segment | First hypothesis | Do not conclude yet |
|---|---|---|
| Both lanes mostly empty before consumers | Upstream supply or transfer is insufficient | The belt speed is the bottleneck |
| One lane packed, the other mostly empty | Uneven lane supply or demand may constrain that item | Half-empty means unlimited capacity for every item |
| Items backed up behind a stopped consumer | Downstream machine, output or storage is blocking flow | More upstream production will fix the blocked exit |
| Both lanes packed and consumers still ask for more | The segment may be near capacity | A visible full belt alone proves its precise delivered rate |
References: Factorio Wiki: Transport belt · Factorio Wiki: Transport belt physics · Factorio Wiki: Inserters
Worked budget: a mixed belt with unequal lanes
Illustrative plan only: one yellow belt carries copper on one lane and iron on the other. The copper consumers together request 9 items per game-second, while the iron consumers request 4. If each item stays confined to its own unstacked lane, the copper lane's 7.5 maximum falls 1.5 per second short. The iron lane is below its own maximum by 3.5; that unused space does not carry copper while the lanes remain separated.
Moving copper to both lanes could raise its belt-only ceiling to 15, but then iron needs another route. A faster belt may also raise capacity, but only if actual upstream supply and downstream transfers support the new rate. This example does not calculate splitter balance, individual inserter speed, recipe timing or a recorded in-game result.
| Lane | Assumed demand | Basic-belt lane ceiling | Arithmetic comparison |
|---|---|---|---|
| Copper | 9 items/s | 7.5 items/s | 1.5 items/s over the ceiling |
| Iron | 4 items/s | 7.5 items/s | 3.5 items/s below the ceiling |
| Combined | 13 items/s | 15 items/s across both lanes | Combined capacity alone hides the copper-lane constraint |
References: Factorio Wiki: Transport belt · Factorio Wiki: Transport belt physics
Follow one item across the boundary
Pause expansion and pick one item that is actually missing from a consumer. Open that consumer to confirm its recipe and input inventory. Then trace the same item back along the belt to its producer: look for the first point where its lane changes from stocked to empty, or the first stationary queue behind a blocked destination.
Inserters are separate transfer steps. Their practical rate varies with the endpoints and conditions; the Wiki's measured examples are not a universal rate for every layout. Confirm orientation, power or fuel, filter settings and a valid pickup/drop target in the installed game before changing the belt tier.
- Record the installed version, active mods and the item the consumer needs.
- Inspect the consumer's input and output: an idle machine with a full output needs a different remedy from an empty input.
- Trace that item backwards through each inserter and belt segment; note which lane contains it and where its visible flow changes.
- Check the producing machine's recipe, inputs, power or fuel and output space. If items are stopped, inspect the next destination before increasing supply.
- Change one identified constraint, then watch the same boundary again. Record whether the consumer's input recovered; do not call the entire factory fixed from one observation.
References: Factorio Wiki: Inserters · Factorio Wiki: Transport belt
Choose the smallest correction
A belt speed upgrade is appropriate only when the relevant lane or shared segment is limiting and the producer can actually feed it. A half-empty line caused by a starved miner stays half-empty if only the belt is replaced. If output is blocked, clear or redesign the downstream destination first.
For planning, use actual recipes, machine counts, clock settings, modules and item mix from your save. Recalculate both lanes independently and leave margin for transfers. When inputs and outputs alternate, a short observation window can be misleading: compare a stable interval with the inventory change at the consumer.
| Verified first constraint | One bounded change | Acceptance check |
|---|---|---|
| Producer lacks material or energy | Restore its specific input or power | The producer resumes output |
| Inserter is pointed incorrectly or cannot transfer | Correct that transfer point | The intended item appears on the next segment |
| Output inventory is full | Restore or expand its downstream destination | The consumer resumes clearing its output |
| A single unstacked lane's required rate exceeds 7.5/s | Route the item differently or evaluate a higher belt tier | Observe delivery and check both lanes again |
References: Factorio Wiki: Transport belt · Factorio Wiki: Inserters
Record a reproducible case
The example above is an analytical ceiling rather than a measured test. To ask for help or evaluate a change, record the exact boundary, actual recipe and a short before/after count. A screenshot showing the whole transfer point and both lanes is more informative than an isolated machine icon; remove private details before sharing.
Game build / mods / simulation conditions:
Item and consumer recipe:
Expected items per game-second on this lane:
First empty or blocked boundary:
Producer input / power / output status:
Transfer direction and settings:
One change / observed inventory before and after:Before you play
- Identify the missing item and distinguish empty input from blocked output.
- Budget each unstacked lane separately; 7.5/s is an upper bound, not observed output.
- Inspect producer and inserter constraints before upgrading belts.
- Recheck one changed boundary and record the result.
Frequently asked questions
Why is an item missing when half the belt is empty?
The item may be confined to a saturated lane while the other lane carries a different item. Compare the specific item's supply and demand; inspect the actual transfer point too.
Does a yellow belt always deliver 15 items per second?
No. Fifteen is the theoretical two-lane maximum for fully compressed unstacked items. Supply, transfers, consumption and simulation conditions can reduce actual delivery.
Is this a tested blueprint?
No. The numerical comparison is editorial arithmetic based on referenced belt physics. It does not claim a played factory, tested blueprint or measured inserter throughput.
Sources & revision notes
Editorial revision: October 28, 2026; not a gameplay test date. The reference notes identify source limits and version differences.
- Factorio Wiki: Transport belt (Community)
Community-maintained game wiki, checked October 28, 2026, for the standard belt's 15-item/s two-lane maximum; not a measurement of this layout.
- Factorio Wiki: Transport belt physics (Community)
Community-maintained physics reference checked October 28, 2026 for the unstacked 7.5-item/s lane maximum and compression assumptions.
- Factorio Wiki: Inserters (Community)
Community-maintained reference checked October 28, 2026 for endpoint and belt-state effects on transfer. Measurements on that page have their own version and setup limits.
- Factorio Friday Facts #449: 2.1 Stable (Official)
Developer release announcement read October 28, 2026. It establishes release context, not that this procedure was played on 2.1.
Added a local two-lane demand calculator with explicit capacity and delivery limits. The worked example remains source-based arithmetic, not a gameplay test.
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