Process yield is a metric used in manufacturing and service industries to quantify efficiency by measuring acceptable output against total input. Rolled Throughput Yield (RTY) is the most precise measure of process efficiency due to its cumulative nature across all sequential steps. RTY shows how often a unit successfully navigates an entire process without correction or rework. This metric is standard within performance improvement frameworks like Lean and Six Sigma.
Understanding Rolled Throughput Yield (RTY)
Rolled Throughput Yield is designed to offer a clear look at how smoothly a product or service flows from start to finish. Traditional metrics, such as final yield or First Time Yield (FTY), often present a misleading picture of efficiency by only counting the final acceptable units. These simpler metrics fail to account for internal inefficiencies, such as the time, materials, and labor spent fixing defects that occur within the process steps.
The purpose of RTY is to capture the compounded effect of internal defects and reworks. It represents the probability that a unit will pass through the entire sequence of process steps defect-free on the first attempt. RTY exposes the waste within a multi-step operation, forcing an organization to address issues at their point of origin, rather than simply correcting them downstream.
RTY is distinctly different from First Time Yield (FTY) because FTY only measures the percentage of units that pass a single step correctly the first time. RTY, however, multiplies the individual first pass performance of every single step. This compounding reveals that the overall system performance is significantly lower than what a simple final inspection yield might suggest.
Defining the Inputs for RTY Calculation
Accurately calculating RTY requires clear definition of the process boundaries and meticulous data collection. The first requirement is to precisely map the entire process and define all sequential steps (S1, S2, S3, etc.). Every action that could potentially introduce a defect must be recognized as a distinct step in the sequence.
The second input is the total number of units that enter the process sequence at the beginning. This initial count serves as the baseline for all subsequent calculations and must remain constant, regardless of any units that are scrapped or reworked. This tracking ensures the final RTY calculation accurately reflects efficiency relative to the starting workload.
The third input is the First Pass Yield (FPY) for each individual sequential step. FPY measures the percentage of units that successfully complete a specific step without requiring rework or scrap. To determine the FPY, track the number of units that passed correctly on the first attempt, then divide this number by the total number of units that entered that specific step. This calculation must be performed for every step.
Step-by-Step RTY Calculation Methodology
The calculation of Rolled Throughput Yield is a straightforward multiplication of the individual First Pass Yields (FPY) for all sequential steps in the process. The overarching formula is: RTY = FPY(S1) × FPY(S2) × FPY(S3) × … × FPY(Sn), where ‘n’ represents the total number of steps. This product of probabilities yields a single number that represents the overall process efficiency.
Before multiplication, the individual FPY for each step must be accurately calculated using a ratio. The formula for FPY is determined by dividing the number of units that passed without defect on the first attempt by the total number of units processed at that station. For example, if 95 units pass a step out of 100 total units processed, the FPY is 95/100, or 0.95.
The FPY values must be converted to their decimal equivalents before multiplication. Using the decimal form ensures the calculation accurately compounds the probability of a unit passing through the entire chain defect-free. The final step involves multiplying all the decimal FPY values together. This results in a final decimal value, which is then multiplied by 100 to express the Rolled Throughput Yield as a percentage. This final percentage represents the yield of the entire process, accounting for the combined effect of internal quality losses.
Practical Example of RTY Calculation
Consider a simplified three-step administrative process for onboarding a new client: S1: Document Submission Review, S2: Background Check Processing, and S3: Account Activation. An organization begins the month with 500 new client applications entering the system.
At the Document Submission Review (S1), 475 of the 500 applications pass without correction. The FPY(S1) is 475/500, or 0.95. The 25 units that required correction represent a first-pass failure, even if they were fixed and passed to the next step.
Moving to the Background Check Processing (S2), all 500 units are processed, and 450 pass without errors. The FPY(S2) is 450/500, yielding 0.90. The 50 units requiring rework introduce inefficiency captured by this lower yield.
Finally, in the Account Activation step (S3), 490 of the 500 accounts are activated correctly on the first attempt. The FPY(S3) is 490/500, resulting in 0.98. If the organization only looked at the final yield, they would see 490 passed units out of 500, suggesting 98% efficiency.
To calculate the Rolled Throughput Yield, the decimal FPYs are multiplied: RTY = 0.95 (S1) × 0.90 (S2) × 0.98 (S3). This yields a final RTY value of 0.8379. Converted to a percentage, the actual RTY for the entire process is 83.79%. This figure is significantly lower than the perceived 98% final yield, illustrating the compounding effect of process inefficiencies.
Interpreting and Applying RTY Results
The final RTY percentage serves as an accurate indicator of overall process health, reflecting cumulative efficiency losses across all steps. A low RTY signals the presence of waste, which translates directly into increased operational costs associated with rework, extended cycle times, and the need for additional resources. This metric provides justification for initiating process improvement projects.
RTY pinpoints the locations of the greatest inefficiency within the system. By examining the individual First Pass Yields, organizations can immediately identify the step with the lowest FPY. This lowest-performing step represents the constraint or bottleneck that reduces the overall process performance.
Targeted improvement efforts should be directed at the step with the lowest FPY, as any enhancement there will provide the greatest return on investment for the entire process. Improving a step from 90% FPY to 95% FPY will have a larger positive impact on the final RTY than improving a step already at 98% FPY. Organizations utilize RTY for internal benchmarking, setting goals to increase the percentage over time, or comparing performance against industry standards.