Free tool
Lead time calculator
Manufacturing lead time is how long a unit takes to get through the process, from the first step to the last, including all the time it waits. Little's Law gives it from two numbers most plants already have: lead time = work in process ÷ throughput. Comparing it with the value-added time shows how much of that lead time is spent actually working on the product.
Lead timeequalsWork in process (WIP) divided by Throughput
Value-added ratioequalsValue-added time divided by Lead time
Every unit between the first step and the last
Average units finished per working day
Turns days into hours and minutes
Work that changes the product, all steps
Pre-filled with the worked example. Lead time comes out in working days because throughput is per working day.
Lead time
6 days
48 working hours, or 2,880 minutes, for a unit to get through.
Value-added ratio
1.25%
Value-added time ÷ lead time
Non-value-added time
2,844 min
Waiting, moving, inspecting
Share of lead time
Next step
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Bring this result to a 45-minute demo and we will show where it fits in LeanSuite's Value Stream Mapping.
How to calculate it
Count the WIP, measure what leaves
Work in process is every unit that has started but not finished: in queues, on machines, in transit and waiting for inspection. A walk along the process with a count sheet gives a good snapshot, the same count a value stream map records between process boxes.
Throughput is the average number of finished units leaving the end of the process per working day. Take it over a few weeks, not one good day.
Working hours per day turn days into hours and minutes, so the lead time can be compared with the value-added time: the minutes of work on one unit, across every step, that change it in a way the customer pays for.
Worked example
Illustrative numbers, not a benchmarkA process with 1,200 units of work in process that finishes 200 units a day, running one 8-hour shift. Adding up every step that changes the product gives 36 minutes of value-added time per unit.
- 1Lead time = 1,200 units ÷ 200 units a day = 6 working days.
- 2In working time: 6 days × 8 h = 48 h = 2,880 minutes.
- 3Value-added ratio = 36 ÷ 2,880 = 1.25%.
- 4Non-value-added time = 2,880 − 36 = 2,844 minutes.
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<iframe src="https://www.theleansuite.com/tools/lead-time-calculator/embed" title="Lead time calculator by LeanSuite" width="100%" height="1020" style="border:0;max-width:1000px" loading="lazy" allow="clipboard-write"></iframe>
<p style="font:13px/1.4 sans-serif"><a href="https://www.theleansuite.com/tools/lead-time-calculator">Lead time calculator</a> by LeanSuite</p>How LeanSuite helps
LeanSuite's Value Stream Mapping turns video of each process step into a current-state map with cycle times, inventory and lead time, and converts the inventory it counts between steps into days of WIP.
See Value Stream MappingRead more
- Lead time in the lean glossary
- What Are the Four Types of Lead Time?
- Value-added time in the lean glossary
- Value stream mapping in the lean glossary
- How to Reduce Lead Time in Manufacturing
- Value-Added vs Non-Value-Added Time in Manufacturing
- How to Improve Throughput Time in Manufacturing
- Current State vs Future State Value Stream Mapping
- Cycle time, throughput time and lead time for one part
FAQ
Lead time calculator: common questions
Divide the work in process by the throughput: lead time = WIP ÷ throughput. With 1,200 units in the process and 200 units finished a day, lead time is 1,200 ÷ 200 = 6 working days. The result is in the same time unit as the throughput, so units per day give days.
Little's Law says that the average number of items in a system equals the average rate they leave it times the average time each spends inside. John Little published a proof in 1961. In a factory it links WIP, throughput and lead time, so knowing any two gives the third. It holds for long-run averages of a stable process, not for any single unit.
The value-added ratio, also called process cycle efficiency, is value-added time divided by lead time. With 36 minutes of value-added work in a lead time of 2,880 working minutes, it is 1.25%. A low ratio means units spend most of their lead time waiting, moving or being inspected rather than being worked on.
Use the average rate at which finished units leave the end of the process, counted in the same units as the WIP and over a period long enough to smooth out daily swings. Use what the process actually delivers, not its rated capacity or the customer's demand, or the lead time will look shorter than it is.
Little's Law gives two levers: hold less WIP at the same throughput, or raise throughput with the same WIP. Cutting WIP is usually the faster one, through smaller batches, pull signals such as kanban and limits on how much work can wait between steps. Halving the WIP in the example to 600 units would cut lead time from 6 days to 3.
Lead time is how long one unit takes to get through the whole process, including all the time it waits. Cycle time is how often a process or station finishes a unit, or the time spent working on one unit at a step. Lead time is usually much longer, because most of it is waiting between steps.
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