Belt Throughput Basics

Hello again! In our first lesson, we established that 'items per second' is the fundamental unit for designing and analyzing your factory. By thinking in terms of flow rates, we can transform factory planning from guesswork into a predictable, solvable process.

We touched on the idea that the transport belts themselves have a maximum capacity, or throughput, also measured in items/s. Today's lesson is short, focused, and absolutely crucial: you will learn the specific throughput values for the three core belt types. Committing these numbers to memory is one of the most high-leverage things you can do to improve your factory-building intuition.

The Three Tiers of Throughput

In the base game, there are three tiers of transport belts: yellow (Transport Belt), red (Fast Transport Belt), and blue (Express Transport Belt). Each tier moves items at a successively higher speed. In the last lesson, a diagram showed their maximum throughput. Now, let's make those numbers precise.

The official Factorio Wiki provides a detailed breakdown of belt physics. The tables on this page are the canonical source for these values.

As the table shows, the maximum throughput for a fully utilized belt is:

• Yellow Belt: 15 items/s (7.5 per lane)
• Red Belt: 30 items/s (15 per lane)
• Blue Belt: 45 items/s (22.5 per lane)

You'll immediately notice a simple pattern: red belts are exactly twice as fast as yellow belts, and blue belts are three times as fast. This linear scaling makes planning and upgrading straightforward. If a yellow belt is running at full capacity and you need more throughput, upgrading it to red will exactly double its capacity.

Deriving Throughput: First Principles

Your interest in first principles and your quantitative background make it worthwhile to look at why these are the numbers. They aren't arbitrary. As we briefly saw in the last lesson, throughput is a function of item density and belt speed.

Let's dig into the wiki page again to see how this works for a basic yellow belt.

As the resource explains:

• Density: On a straight belt, items are packed at a density of 4 items per tile, per lane.
• Speed (Yellow Belt): A yellow belt moves at 1.875 tiles per second.

Therefore, for a single lane of a yellow belt:

For both lanes, this is simply doubled to 15 items/s. The red and blue belts have speeds of 2x and 3x this base speed, respectively, leading directly to their 30 and 45 items/s throughput values.

This connection between the game's physical simulation and the resulting macroscopic values is what allows for such precise factory planning.

Visual Confirmation

It's one thing to see the numbers in a table, but it's another to see them verified in the game. The following image shows an in-game setup measuring the throughput of a fully saturated blue belt.

The measurement is displayed in items per minute. A quick conversion confirms our value:

This demonstrates that the theoretical maximum is achievable in practice, provided the belt is fully loaded.

Conclusion

This lesson was short, but the information is dense and foundational. Knowing these numbers by heart will allow you to quickly assess bottlenecks and plan your logistics at a glance.

Key Takeaways:

• The three main belt tiers have the following maximum throughputs:
  • Yellow: 15 items/s
  • Red: 30 items/s
  • Blue: 45 items/s
• These values follow a simple 1x, 2x, 3x progression, making upgrades predictable.
• Throughput is derived from the game's physics: Throughput = Density × Speed.

We've now defined our universal unit (items/s) and established the capacity of our logistical tools. However, achieving this maximum capacity is not automatic. A belt with gaps between items will have a lower throughput than its theoretical maximum. In our next lesson, we will explore the concept of belt compression and why it is critical for ensuring your belts are delivering their full potential.