Quality

Deploying Rolled Throughput Yield Across the Whole Line

Six stations at 96 percent each roll to 78 percent. How to run the yield waterfall that keeps station metrics honest and finds the real constraint.

Rolled throughput yield exposes the lie in station-level yield reports. Six operations each running a comfortable 96 percent multiply to 0.96 to the sixth power, 78.3 percent, meaning barely three of four units clear the whole process untouched. Every one of those station managers hits their target while the plant eats 22 percent of its volume in scrap and rework. On a line starting 500,000 units a year at $18 conversion cost, the gap between station pride and process truth is worth roughly $1.9 million in defect handling. RTY is the number that decides whether the plant is actually good or just locally good.

The math is multiplication, but the inputs need honesty. Each operation's first-time yield is units passing without rework divided by units entering. Five operations at 99.2, 97.5, 95.8, 98.9, and 96.4 percent give RTY of 0.992 times 0.975 times 0.958 times 0.989 times 0.964, which is 88.4 percent. The Rolled Throughput Yield calculator chains the multiplication and shows which station drags the product down. Two rules keep it honest: reworked-then-passed units do not count as first-time passes, and every operation reports on the same time window, because mixing weekly and monthly yields makes the rolled number fiction.

Benchmarks scale with step count, which is the point. A 5 step process at 95 percent per step rolls to 77 percent; at 99 percent per step, 95 percent; at 99.9 percent, 99.5 percent. Short machining routings commonly roll 85 to 95 percent. A 12 station assembly line at typical station yields rolls 70 to 85 percent. Semiconductor fabs with 400 plus steps need per-step yields above 99.98 percent just to ship half their starts, which is why they invented most of yield management. Rule of thumb: your required per-step yield is the target RTY raised to the power of one over the number of steps.

Improve RTY by attacking the lowest station first, but weight by cost position. A point of yield at final assembly, where the unit carries $200 of accumulated value, is worth 8 to 10 times a point at the first operation carrying $22. Second lever, reduce step count: every operation eliminated through combined fixturing or design change removes a yield tax forever; cutting a 10 step route to 8 at 97 percent per step lifts RTY from 73.7 to 78.3 percent with zero station improvement. Third, stabilize handoffs; 10 to 20 percent of multi-station defects are damage and contamination between operations, owned by nobody.

Failure modes: the worst is station-level sandbagging, where operations quietly rework and pass units, reporting 99 percent while feeding defects forward. Reconcile RTY against end-of-line first pass yield monthly; a gap above 3 points means somebody's yield is fiction. Second, averaging RTY across products with different routings, which blends a 65 percent problem into an 85 percent portfolio. Third, ignoring measurement operations: a test station that falsely fails 2 percent of good units costs the same capacity as a real 2 percent defect rate. Fourth, celebrating RTY gains that came from slowing the line; always read RTY next to throughput.

Cadence: weekly, publish the yield waterfall, every station's first-time yield and the rolled product, on one chart at the value stream board; the lowest bar gets a named owner and a 14 day action. Monthly, review RTY by product family against a glide path, for example 78 to 85 percent over 12 months, and run the reconciliation against end-of-line data. Quarterly, revisit the routing itself: which steps can merge, which inspections can move upstream, which station deserves capital. Daily management stays at the station level with FPY; RTY is the weekly and monthly integrator that keeps station metrics honest.

World-class RTY depends on routing length, so the marker is per-step discipline: mature plants hold every operation above 99 percent first-time yield and know their bottom three stations without opening a laptop. A 10 step line at that standard rolls above 90 percent, and the best short-route operations sustain 95 to 98 percent RTY for years. Improvement pace: plants running the weekly waterfall typically gain 5 to 10 points of RTY in the first year, worth $500,000 plus on mid-volume lines, then 2 to 4 points a year after. When RTY, FPY, and scrap dollars triangulate within a few percent, your data finally tells one story.

Published 2026-07-02.