Build a left-to-right value stream map: chain process boxes, set cycle time, changeover, uptime and operators, and place inventory buffers between steps. The tool computes takt time, flags bottlenecks, and headlines lead time, value-added time and Process Cycle Efficiency. Everything runs in your browser.
Tip: edit any cell directly. The inventory triangle (โฒ) before each process holds WIP in pieces; its days-of-inventory = pieces รท daily demand. Any process whose C/T exceeds takt time is flagged red as a bottleneck โ it cannot keep pace with customer demand.
Value Stream Mapping (VSM) is the core Lean tool for visualizing the flow of material and information required to bring a product to the customer. This builder lets you chain process boxes left-to-right, record each step's cycle time, changeover, uptime and operators, and place inventory (WIP) triangles between steps. It then computes takt time, total value-added time, total lead time, Process Cycle Efficiency (PCE) and total WIP โ the headline numbers every continuous-improvement event starts from.
A VSM is a flowchart of every step โ value-adding and non-value-adding โ that a product passes through, drawn with a standardized icon language. Process boxes represent operations; data boxes beneath them carry the key metrics (C/T cycle time, C/O changeover, uptime %, operators, scrap). Inventory triangles (โฒ, labeled "I") sit between processes and show where work-in-process piles up โ these queues are usually where most lead time hides. A timeline ladder runs along the bottom: the lower "value-added" steps show process cycle times, and the upper steps show how long material waits as inventory. The difference between the two is the improvement opportunity. The goal of mapping is to see the whole flow at once so you can attack waste systematically rather than locally optimizing one station.
Lean practice draws two maps. The CURRENT STATE map documents how the value stream actually operates today, queues and all โ you walk the floor and record real numbers, not the standard work assumptions. The FUTURE STATE map is the redesigned flow you want to achieve: pull systems and supermarkets replacing push, processes balanced to takt, continuous flow cells, reduced changeover (SMED) so smaller batches are economical, and inventory cut to deliberate, sized buffers. The gap between the two maps becomes your improvement plan (the "kaizen burst" actions). This tool builds the kind of map you would use for either state โ edit the cycle times, batch sizes and inventory to model a future state and watch PCE rise as you remove the queues.
Takt time = available work time per day รท customer demand per day. It is the pace at which you must complete one unit to exactly meet demand โ the heartbeat of the line. Cycle time (C/T) is how often a finished piece actually comes off a given process. If any process C/T exceeds takt, that station cannot keep up and becomes a bottleneck (flagged red here). Lead time is the total elapsed time one piece spends in the value stream from raw material to shipment โ dominated by waiting in inventory queues, not by processing. Use Little's Law to connect them: Lead Time = WIP รท throughput. Cutting WIP directly cuts lead time. This is why reducing inventory between steps is the fastest lever on responsiveness.
Process Cycle Efficiency = Value-Added Time รท Total Lead Time ร 100%. It is the single most revealing number on a value stream map. Value-added time is the sum of process cycle times โ the time actually spent transforming the product in a way the customer would pay for. Lead time includes all the waiting in between. Most unimproved manufacturing value streams run a PCE of 1โ10%; office and administrative processes are often well under 1%. World-class continuous-flow lines reach 25% or more. A low PCE is not a sign of slow machines โ it means material spends almost all its time waiting in queues. The improvement strategy is therefore almost always to shrink inventory and batch sizes (which slashes lead time) rather than to speed up individual operations. Watch the PCE figure climb in this tool as you reduce the inventory triangles between steps.
Takt time = net available work time per day รท customer demand per day. For example, 27,000 seconds of available time and 900 units demanded gives a takt of 30 seconds per unit โ you must complete one good unit every 30 seconds to meet demand. Net available time excludes breaks, lunches and planned downtime, but not unplanned downtime (that is captured separately in uptime).
Takt time is set by the customer โ it is the required pace (demand-driven). Cycle time is set by the process โ it is the actual pace at which a station produces. You compare them: if cycle time is at or below takt, the process can keep up; if cycle time exceeds takt, it is a bottleneck and cannot meet demand without overtime, extra shifts or rebalancing. The ideal is to balance every process cycle time to just under takt.
Because material spends the overwhelming majority of its time waiting in inventory queues between processes, not being worked on. A part might take 3 minutes of actual processing but sit in WIP for 5 days. This gap is exactly what a value stream map exposes โ and it is why Process Cycle Efficiency (value-added รท lead time) is typically only a few percent. Cutting WIP, not speeding up machines, is the fastest way to shrink lead time.
Days of inventory = pieces on hand รท average daily customer demand. 1,200 pieces in front of a process that ships 900 units/day equals about 1.3 days of inventory. Summing the days across every triangle gives the inventory portion of lead time, which usually dwarfs the value-added (processing) portion.
It depends on the process type. Traditional batch manufacturing often runs 1โ10%. Continuous-flow assembly can reach 20โ25%. Highly optimized, mistake-proofed flow lines may exceed 30%. Office/transactional processes are frequently below 1% because work waits in approval queues and inboxes. There is no universal target โ the point is to measure your current PCE, then design a future state that raises it by removing queues and batching.