Rolled throughput yield (RTY) is the probability that a single unit passes through every step of a process without a defect, rework, or correction. It’s calculated by multiplying the first-time yields of each individual process step together. The result is almost always lower, sometimes dramatically lower, than the yield number most organizations track. That gap is exactly why RTY matters.
How RTY Differs From Standard Yield
The most common way to measure process quality is first time yield (FTY), which simply divides good outputs by total inputs at the end of a process. If 100 units go in and 100 come out, FTY is 100%. The problem is that FTY ignores everything that happened between start and finish. If 5 units were caught and reworked at step two, and another 5 were fixed at step four, FTY still reports a perfect score. The customer got 100 good units, so FTY sees no issue.
RTY tells a different story. It tracks defects at every individual step, not just at the final gate. In the same scenario, RTY would capture both of those 5% defect rates and multiply them together: 0.95 × 0.95 = 0.9025, or about 90%. Instead of a process running at 100% compliance, RTY reveals one that wastes roughly 10% of its resources on corrections the customer never sees but the company still pays for.
FTY is unit-sensitive. It counts whether each finished unit passes or fails. RTY is defect-sensitive. It counts the number of defects found and fixed along the way, even if the final product looks fine. That distinction makes RTY a far more honest measure of how well a process actually performs.
The Hidden Factory
The rework, retesting, and correction that happens inside a process but never shows up in final yield numbers is called the “hidden factory.” It’s hidden because traditional metrics don’t capture it. Units get fixed and move on, and the end-of-line data looks clean. But those fixes consume time, labor, materials, and capacity. They represent real costs that erode profit margins without appearing in standard quality reports.
RTY is specifically designed to expose the hidden factory. By requiring you to track pass rates at each step, it forces visibility into where defects actually originate. A case study published by the American Society for Quality examined a cashew processing operation where a previously unidentified rework loop was quietly draining productivity and profitability. Applying RTY across the production stages revealed the waste, allowed the team to pinpoint the problem steps, and led to measurable gains in output. The takeaway wasn’t unusual: most organizations that calculate RTY for the first time discover their processes are significantly worse than they believed.
How to Calculate RTY
The formula is straightforward. You find the first-time yield for each step in your process, then multiply them all together.
RTY = FTY₁ × FTY₂ × FTY₃ × … × FTYₙ
Each step’s first-time yield is the proportion of units that passed through that step correctly on the first attempt, with no rework, scrap, or correction. If a step processes 200 units and 10 need to be reworked before moving on, that step’s FTY is 190 ÷ 200 = 0.95, or 95%.
A Five-Step Example
Imagine a process with five steps. Each one has a 95% first-time yield, which sounds solid in isolation. But multiplication is unforgiving:
0.95 × 0.95 × 0.95 × 0.95 × 0.95 = 0.774
The rolled throughput yield is 77.4%. Nearly one in four units encounters a problem somewhere along the way. Each step looked healthy on its own, but the cumulative picture is a process with significant hidden waste. This compounding effect is the core insight of RTY: small defect rates at individual steps become large quality problems across the full process. A ten-step process with 95% yield at each step drops to just 60%.
RTY and Sigma Levels
In Six Sigma methodology, process capability is often expressed as a sigma level, which corresponds to a specific yield percentage and defect rate. RTY connects directly to these benchmarks:
- 3 Sigma: 93.32% yield, roughly 66,807 defects per million opportunities
- 4 Sigma: 99.38% yield, roughly 6,210 defects per million opportunities
- 5 Sigma: 99.98% yield, roughly 233 defects per million opportunities
- 6 Sigma: 99.99966% yield, roughly 3.4 defects per million opportunities
Most organizations operate between 3 and 4 sigma. The jump from 3 to 4 sigma looks small in percentage terms (about 6 points) but represents a tenfold reduction in defects. RTY gives you the honest number you need to place your process on this scale. If you’re using FTY and it says 99%, you might think you’re near 4 sigma. RTY might reveal you’re actually closer to 3.
Why RTY Matters for Improvement
The real value of RTY isn’t the number itself. It’s that the calculation forces you to collect data at every process step, which immediately tells you where the problems are. If your five-step process has yields of 99%, 98%, 97%, 95%, and 99%, you know that step four is the weakest link. Without RTY, you might only see the final output and have no idea where to focus improvement efforts.
RTY also changes how teams prioritize. A process step with 95% first-time yield might seem acceptable when viewed alone. But when you see its impact on the overall RTY, especially in a process with many steps, that 5% defect rate becomes urgent. Teams that track RTY consistently tend to shift their attention from catching defects at the end of the line to preventing them at the source, which is where the largest cost savings and capacity gains come from.
The metric also provides a clear before-and-after comparison for any improvement project. If you redesign a process step and its first-time yield goes from 92% to 98%, you can instantly see how that change flows through to the overall RTY. That makes it easier to justify improvement investments and demonstrate their impact in terms leadership understands: fewer resources wasted on rework, higher effective capacity from the same equipment and people, and better margins on every unit produced.