Bottleneck Analysis Calculator: Find the Constraint
Every production line has a bottleneck: the resource with the least capacity relative to what it must process. Improving anything else does not raise output. This calculator compares the weekly capacity of three resources against demand and shows which one is the constraint.
Your numbers
Units the customers require per week.
For example two 8 hour shifts for five days is 80.
Availability times performance times quality.
Your results
Assumes a serial line, no scrap between steps and the same OEE on every resource. Adjust the time per unit upward to reflect scrap or rework loops.
Bottleneck utilization versus weekly demand
Sweeps Weekly demand from 100 to 700, holding your other inputs fixed.
Find your real constraint from ERP data
Optional: a brief review of how routings and reported times in your ERP can reveal the constraint.
Optional. The tool and every export work without this. No spam.
How to use it
Enter weekly demand, the scheduled hours per week and an average OEE. Then enter the process time per unit and the number of parallel machines for each of three resources, for example machining, assembly and test. The calculator converts everything to units per week for each resource and picks the lowest as the bottleneck. Try raising demand or adding a machine to see how the constraint moves. Use the chart to see where the bottleneck reaches 100 percent utilization.
- Use actual time per unit including setup spread over the lot.
- Use measured OEE per resource if you have it; this tool uses one average.
- Combine operations on the same machine into one resource.
The method
Capacity per week equals scheduled minutes times OEE times machine count divided by process minutes per unit. The resource with the lowest capacity is the bottleneck, in line with the Theory of Constraints, which says that an hour lost at the constraint is an hour lost for the whole system. Utilization is demand divided by bottleneck capacity. Throughput is limited to the lower of demand and bottleneck capacity. The remaining resources have protective capacity, which is what lets the constraint stay busy despite variation.
Worked example
With 80 scheduled hours and 75 percent OEE, resource A with two machines at 12 minutes per unit gives 600 units a week. Resource B with one machine at 9 minutes gives 400, and resource C with one machine at 5 minutes gives 720. Resource B is the bottleneck at 400 units. Demand of 380 means it runs at 95 percent, with almost no headroom. Adding a second machine at B raises its capacity to 800 and moves the constraint to A at 600. That is the pattern: fix the constraint and the next one appears.
Common mistakes
A frequent error is to use nameplate capacity instead of demonstrated capacity, which overstates every resource. Another is to improve a non-constraint, such as speeding up resource C, and expect more output. Also watch for shifting bottlenecks caused by product mix, where different products load different machines. In that case, run the calculator for each mix scenario, or weight the process times by the expected mix.
Frequently Asked Questions
How do I identify a bottleneck in production?
Compare the effective capacity of each step in units per period. The step with the lowest capacity, or the one with the highest utilization and the longest queue in front of it, is the bottleneck. Confirm on the floor: downstream stations wait on it while upstream stations pile up work.
Why does the bottleneck matter for scheduling?
The bottleneck sets the output of the whole system, so the schedule should be built around it. Keep it fed, avoid starving it, and protect its time from changeovers, breaks and quality problems. Other resources can then be scheduled to support it.
What utilization is safe for the bottleneck?
Queues grow quickly as utilization approaches 100 percent, so many planners aim for roughly 85 to 90 percent on the constraint while keeping it never idle. The right figure depends on variability, so treat the target as a starting point to adjust from experience.
Can the bottleneck move?
Yes. It can move when you improve the constraint, when product mix changes, or when a machine goes down. That is why you recheck capacity after every material change and keep protective capacity at the other resources.
If you want the bottleneck identified from live routings, work center calendars and actual reporting in your ERP, Netray can help you build that analysis over your data.
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