Yamazumi Chart

A yamazumi chart is the lean tool for line balancing. Most multi-operator lines have at least one station that is overloaded and at least one that is underloaded, and the overloaded one becomes the bottleneck that paces the whole line. Without a yamazumi, the imbalance is invisible; the line lead sees that station three is slow but cannot tell whether that is because of operator skill, element difficulty, or assignment. With a yamazumi, the imbalance is immediately legible, and the conversation moves from blame to design.

"The line is only as fast as the tallest stack on the chart. Move blocks until the stacks line up."

How a yamazumi chart works

A yamazumi chart starts with element-level time data, almost always produced by a time study. The work to be done in one cycle is broken into elements, each with a measured time. The total work in a cycle is then assigned across operators or stations.

The chart itself is a stacked bar chart:

• One vertical bar per operator or station.
• Inside each bar, work elements are stacked from bottom to top, each block sized in proportion to its element time.
• A horizontal line is drawn across the chart at takt time, the rhythm dictated by customer demand.

The visual immediately surfaces line imbalance. Operators whose stacks rise above the takt line are overloaded; they will be the bottleneck and the line will pace at their rate. Operators whose stacks fall below the line have absorbable capacity. The team can then move elements between operators (the blocks in the chart) until the stacks all line up close to takt, with a small safety margin for variation.

The chart is built with the operators in the room, not from a desk. They know which elements actually require setup time, which require skill, and which can be done by anyone. The lifted element has to fit physically at the receiving station, not just numerically on the chart.

A yamazumi is not a one-time exercise. Takt changes with demand, mix changes with the schedule, and the line has to be rebalanced as conditions shift. Most lean shops review their yamazumi monthly and rebalance whenever takt moves more than 10 percent.

Where a yamazumi chart fits on the shop floor of a small manufacturer

Imagine a 30-person small electronics assembly shop running a four-station line for a power-tool customer. Output has been below target for two months, holding around 26 units per hour against a goal of 32. The shift lead has been suspecting station three. Before adding pressure on the station-three operator, she runs a time study and builds a yamazumi.

The time study breaks the assembly into 19 elements. The yamazumi shows the four bars side by side with the takt line at 110 seconds:

• Station one: 98 seconds.
• Station two: 95 seconds.
• Station three: 132 seconds, clearly above the takt line.
• Station four: 71 seconds, well below.

The team moves two short elements from station three to station four (a connector seating and a label application). On paper, station three drops to 108 seconds and station four rises to 95. The team verifies the move physically fits at station four, makes the change, and runs the line. The next shift hits 31 units per hour. Within a week, output stabilizes at 32. The station-three operator was not the problem; the assignment was.

That is a yamazumi at small scale. A piece of butcher paper, a stack of elements, a takt line, and a rebalance that no one would have proposed without the chart on the wall.

Common mistakes with yamazumi charts

• Building from estimates. The bars look authoritative even when the underlying numbers are guesses. Run a real time study before drawing the chart.
• Balancing strictly to takt with no buffer. Real shops need a small safety margin for variation. Aim for 90-95 percent of takt at the heaviest station.
• Moving elements without checking physical fit. An element that fits on the chart may not fit at the workstation. Confirm the move with the operators before committing.
• Treating the chart as one-time. Takt changes with demand. The yamazumi has to be revisited monthly, or whenever the schedule shifts.
• Using it to set targets without operator input. The chart is descriptive. The decisions about what to move are best made with the people who run the line.

Yamazumi chart and related Lean tools

A yamazumi chart depends on element-level data from a time study. The detail behind each operator's stack is documented in a standard work combination table, which sequences manual, walk, and machine time for one operator. The horizontal takt line on the yamazumi reflects takt time, which ultimately comes from customer demand. The element-by-element time data also feeds cycle time calculations and standard work documentation.