1
Define the process
Set start and end points. Use times for the same order or batch at each operation.
Your inputs
The methods use different inputs for the same defined process.Please enter a valid value within the stated range.
parts
Time average within the defined process, rather than one snapshot.Please enter a valid value within the stated range.parts/h
Completed parts per hour within the same process and on the same time basis.Please enter a valid value within the stated range.Minutes for the same order or batch. Enter total processing time for the entire batch being tracked. Separate queue time before an operation from storage time between operations.
Lead time
Lead time
Flow efficiency
Processing time
Other time
Breakdown
Processing
Setup
Queue
Storage
Transport
Review scenarios
The first scenario applies to time addition, the second to Little’s Law. Lower WIP shortens lead time only if throughput stays unchanged.
20% less queue and storage time: new lead time
20% less WIP at unchanged throughput: new lead time
Recommendations
Review the largest time component first. Assign every period once. Compare orders and batches only with matching process boundaries and time bases.
Please check your inputs. Required values cannot be blank.
Lead Time Calculator: Guide
2
Enter times or averages
Add setup and processing to queue, storage and transport time. Little’s Law instead uses average WIP and average throughput.
3
Review time shares
Flow efficiency here is processing time divided by lead time. Setup is excluded from processing. Little’s Law alone cannot determine flow efficiency.
The formulas at a glance
Time addition
Lead time = Σ(P + S + Q + W + T)All times in minutes, across all operations.
Flow efficiency
Σ processing ÷ lead time × 100Only processing time is included in the numerator.
Little’s Law
Lead time = average WIP ÷ average throughputStable process, matching system boundaries and time basis; parts/h gives hours.
Worked example: two operations
Operation 1 takes 30 minutes of processing, 10 of setup, 60 in queue and 5 in transport. Operation 2 takes 20 minutes of processing, 5 of setup, 30 in queue and 10 in storage.
| Item | Calculation | Result |
|---|---|---|
| Operation 1 | 30 + 10 + 60 + 0 + 5 | 105 min |
| Operation 2 | 20 + 5 + 30 + 10 + 0 | 65 min |
| Lead time | 105 + 65 | 170 min |
| Flow efficiency | 50 ÷ 170 × 100 | 29.41% |
| Little’s Law | 500 parts ÷ 100 parts/h | 5 h |
Limits of the calculation
- Time addition models a serial process. Overlapping operations, transfer batches and parallel machines require a process schedule.
- Avoid counting downtime again if the same minutes are already included in queue time. Cycle time per part is distinct from order lead time.
- Little’s Law gives an average. It does not predict the delivery date of one order.
Frequently asked questions
How do you calculate manufacturing lead time?
For a serial process, add processing, setup, queue, storage and transport time across all operations.
What is flow efficiency?
Here it is processing time divided by lead time. Setup is excluded from the numerator. Align definitions before comparing figures.
When does Little’s Law apply?
For a stable, defined process with matching averages: average WIP = average throughput × average lead time.
Is lead time the same as cycle time?
Lead time covers passage through the process. Cycle time describes one recurring production cycle.
Which time basis should I use?
Use operating hours or calendar hours consistently. Throughput per operating hour and WIP measured across calendar days need reconciliation.
Calculation source: John D. C. Little: Little’s Law as Viewed on Its 50th Anniversary (2011)