Production lead time calculator

A job's production lead time starts when it's released to the floor and ends when it's finished. At every operation, the time splits into four parts, plus any time spent outside:

Queue time

Waiting in front of a machine or a person for its turn. Usually the largest part

Setup time

Getting the machine ready for this job: tools, fixtures, programs, first-piece checks

Run time

Actually making the batch: the only part a customer would call work

Move and wait time

Moving to the next operation, and waiting for material, a drawing, an inspection or an approval

Outside processing

Days at job workers for plating, heat treatment, grinding and similar processes

Add the four parts for every operation, then add the days outside:

Lead time = Σ (queue + setup + run + move) for each operation + days at job workers

An example (illustrative numbers): a job passes through 5 operations. Each takes about 3 hours of setup and run time, and waits about 14 hours before it starts. The floor works two shifts, 16 hours a day, and the job spends 3 days at a plating job worker. That's 15 hours of work and 70 hours of waiting, or about 5.3 working days inside, plus 3 days outside: about 8.3 days in all. The job is being worked on for about 11% of that time.

From your totals instead: if you know how many jobs are open and how many you finish on an average day, Little's law gives the average lead time directly:

Lead time (days) = open jobs ÷ jobs finished per day

120 open jobs and 8 finished a day means a new job takes about 15 days. Our work in progress calculator does this sum and shows the cash tied up in those open jobs.

These terms get mixed up, and they answer different questions:

A job can have a short cycle time and a long lead time: each piece takes two minutes on the machine, but the batch waits days for its turn. That gap is where most delivery problems start.

On a busy floor with many different jobs, a job usually spends far more time waiting than being worked on. It waits for the machine to free up, for the setter, for material, for the latest drawing, for an inspection, or for someone to decide whether it's next. None of that time shows up on a machine's utilisation report, so it's easy to miss.

The calculator above shows the share for your own numbers. If the job is being worked on for a small part of its lead time, faster machines won't help much. Shorter queues and quicker answers will.

• Start fewer jobs at once. Every extra open job lengthens every queue. Release a new job when the floor has room for it, not when the order arrives.

• Keep the bottleneck busy. The slowest operation sets the pace for everything. Make sure it never waits for material or a decision. More on finding it in the wandering bottleneck.

• Move smaller batches. Send part of a batch to the next operation as soon as it's done, instead of waiting for the whole lot.

• Shorten changeovers. Quicker setups make small batches affordable. It's one of the core ideas of lean manufacturing.

• Decide priorities by due date. Not by whoever calls loudest. See what to run next.

• Answer questions faster. A job waiting for a drawing revision, a material decision or a customer's approval is waiting for information. When that information is scattered across WhatsApp, email and Excel, the wait grows.

• Plan the job-worker trips. Batch the trips sensibly, track what's out and when it's due back, and follow up before it's late.

You don't need software to start. In a sheet, record the date each job is released and the date it's finished. The difference is its lead time. After a few weeks, look at the middle value (the median) and at the slowest jobs, and ask where they waited.

To see where the time goes, add a column for the date each job reaches each operation. A barcode on every job card, scanned at each stage, saves retyping: the bulk barcode generator prints the labels from your job list. Choosing software to track it? Read what an MES does, and when you need one.