Lead Time

Lead time is the metric your customer actually feels. They do not see your cycle times, your changeover hours, or your machine utilization. They see the gap between when they hit send on the purchase order and when the truck pulls up to their dock. In most small shops that gap is mostly waiting, and most of the waiting is invisible until someone draws a map of it.

"The customer's clock starts at the order. Everything between then and the dock is lead time, whether you are working on it or not."

How lead time works

Lead time is the sum of every minute that passes between order and delivery. It breaks into a handful of buckets: order-processing time, material lead time from suppliers, queue time between operations, cycle time at each operation, inspection and rework time, and outbound logistics. The trap in most small shops is treating lead time as the sum of cycle times. The truth is closer to the opposite: queue time usually dwarfs cycle time by an order of magnitude.

A useful way to see it is the value-add ratio. Take the total lead time, then add up the minutes of actual value-added work inside it. In a typical SMB shop, value-added work is one to five percent of lead time. The other ninety-five percent is waiting. That ratio is why lean treats lead time, not unit cost, as the central productivity metric. Cutting cycle time on a single operation rarely moves lead time. Cutting queue time between operations always does.

The other lever is order-entry and material lead time. Many shops cannot see how long the order sat in someone's inbox before paperwork moved, or how long the raw stock waited at a supplier dock. Both of these are lead time. Both are addressable. A weekly delivery from a steady supplier beats a monthly delivery every time, even if the per-unit cost is slightly higher, because the cash-to-cash cycle compresses.

Where lead time fits on the shop floor

Picture a 25-person fab shop running sheet metal enclosures for a small electronics OEM. Quoted lead time is five weeks. The owner thinks the shop is slow because the press brake is the bottleneck. A lead-time map tells a different story. Material arrives nine days after the PO. Parts sit one to three days in a WIP cart between laser and brake, another two days between brake and weld, and an average of four days in the ship-ready rack before paperwork releases them.

Out of those thirty-five days, fewer than two days are actual processing. The brake is not the problem. The carts are. A modest WIP limit between operations, a weekly delivery instead of monthly from the steel supplier, and a daily ship-release meeting cut the quoted lead time from five weeks to two without anyone touching a machine. That is what a lead-time fix usually looks like in a small shop. Less machine, more flow.

Common mistakes with lead time

• Quoting lead time from processing hours. Customers feel calendar days, not machine hours. A shop that quotes "eight hours of work" as "one week" will lose the bid to a competitor quoting calendar reality.
• Cutting cycle time without cutting queue time. Saving four minutes on a mill cycle does nothing if parts sit two days in the next cart. Fix the spaces between operations first.
• Padding every quote for worst-case. Padding makes short orders uncompetitive. Better to size buffer capacity and quote real lead time.
• Ignoring order-entry time. The order that sat two days in the sales rep's inbox is two days of lead time the customer already feels.
• Confusing lead time with throughput time. Throughput time starts when work begins. Lead time starts when the order lands. The gap between them is usually order-entry and procurement.

Lead time and related Lean tools

Lead time is the umbrella metric most lean tools serve. Cycle time is the per-operation time inside it. Throughput time is the work-in-progress portion of it. Takt time is the demand pace it has to keep up with. Cutting lead time usually means attacking queue time with a pull mechanism, which is where pull systems and kanban come in. On-time delivery is the customer-facing outcome lead time controls.