Heijunka explained
Heijunka, or production leveling, means building a small, repeating mix of every product instead of long runs of one product at a time. A line that builds A B C, A B C carries less stock and makes customers wait less than a line that builds AAA, BBB, CCC.
Matt Savas · Reviewed October 2026 · About 6 minutes
What heijunka is
Heijunka is Japanese for leveling. In the Toyota Production System it means two things. The line builds about the same total amount every day, and it builds the same mix of products through the day instead of in big runs.
It is what lets flow and pull work in a plant that makes more than one product. Each step upstream sees a steady, predictable demand, so it can keep only a small amount of stock.
The problem with big batches
A line that makes three products will often make them in long runs: a week of A, then a week of B, then a week of C. There are few changeovers and the schedule looks tidy. But finished goods pile up, and a customer who wants C on Monday waits until Friday.
Here is a small version. A line builds nine units: three each of products A, B and C. Customers want about the same amount of each. In big batches (AAA, BBB, CCC) there are 2 changeovers, but up to 3 units of one product sit in stock, and a customer who wants C waits 6 slots. In a level mix (A B C, A B C, A B C) the line builds the same nine units. Stock of any product never goes above 1, and no customer waits more than 2 slots. The line now changes over 8 times instead of 2.
Build order for one cycle
- Peak stock
- 3
- Longest wait
- 6slots
- Changeovers
- 2
What leveling gets you
- Less stock. Short runs mean finished goods don't pile up waiting to ship. Peak stock drops from a full batch to about one unit, which frees cash and floor space.
- Shorter waits. Every product is made every cycle, so any order can be filled within a slot or two.
- Steadier demand upstream. A line that builds in big runs pulls parts from suppliers in big lumps, and each tier up the chain makes the swings worse. A level schedule pulls parts evenly, so suppliers and every kanban loop that feeds the line can run at a steady pace.
Why leveling needs quick changeover
In the example, leveling took the line from 2 changeovers to 8. If each changeover takes an hour, that costs six hours of capacity. Leveling only pays when changeovers are short. That is why heijunka and quick changeover (SMED) are taught together. The shorter your changeovers, the smaller your batches can be.
How to build a level schedule
Real demand is rarely an even split. To turn an uneven mix into a level schedule, follow four steps.
- Work out takt. Divide the available time by total demand. Takt time is the pace the customer sets. Compare it with the cycle time you measure at each station. The Takt Time Calculator does the math.
- Set the pitch. Multiply takt by the number of units in one pack or container. The pitch is how often the line gets a new piece of work.
- Find the mix ratio. Reduce each product's demand to the simplest ratio.
- Spread the work evenly. Space each product across the cycle by its share, and load it into the heijunka box: one row per product, one column per pitch. Release one column every pitch.
Say a line has a 480-minute shift and customers want 6 of A, 3 of B and 3 of C. Total demand is 12, so takt is 480 ÷ 12 = 40 minutes. With one unit per pitch, the pitch is also 40 minutes. The mix ratio is 2 : 1 : 1, so the level build order is A B A C, repeated three times. Change the demand below to see the box level a different mix.
- Demand per shift
- 12units
- Mix ratio (A : B : C)
- 2 : 1 : 1
- Takt = 480 ÷ 12
- 40min
- Pitch = takt × 1
- 40min
Level build order
Heijunka box: one column every 40 minutes
Swipe sideways to see all 12 columns.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
A | ||||||||||||
B | ||||||||||||
C |
Release one column every pitch, left to right.
Leveling outside the factory
The same idea works anywhere work arrives in lumps. A support team that saves its tickets for Friday, a finance team that does all its closing at month-end, and a hospital that books every elective surgery for Monday all have unlevel schedules. Spread the same work evenly through the week, and the peaks, the overtime and the waiting come down.
Common mistakes
- Leveling before cutting changeover time. More changeovers with long setups use up time the line needs. Shorten changeovers first, then make the runs smaller.
- Leveling the mix but not the volume. If the daily total swings with every order, the box can't keep the line steady. Set a daily volume from average demand, and cover day-to-day swings with a small store of finished goods.
- Releasing work early. If the team pulls the next column before its pitch is up, the line drifts back into batches. Release one column per pitch and no sooner.
How to start
Pick one line that makes a few products with steady demand. Time its changeovers and shorten the longest ones. Then work out takt and pitch, and lay out the box with the free Heijunka Box Designer. Start with a mix of short runs, such as AA BB CC, and make them smaller as changeovers get faster.
Frequently asked questions
- What is heijunka?
- Heijunka is production leveling. The line builds a small, repeating mix of products every cycle (A B C, A B C) instead of long runs of one product (AAA, BBB, CCC). It levels both the total volume and the mix of work.
- Why is leveling better than running big batches?
- A level schedule keeps finished-goods stock low and lets any product be filled within a slot or two. It also pulls parts from suppliers evenly, so they can run at a steady pace. Big batches pile up stock and make most customers wait through a whole run.
- What is the difference between heijunka and one-piece flow?
- One-piece flow is about how a single unit moves through the process steps. Heijunka is about the order and mix of products you schedule onto the line. Plants use them together: flow moves each unit, and heijunka decides which unit comes next.
- Why does heijunka need quick changeover?
- Leveling the mix means more changeovers. In the nine-unit example, two became eight. That only pays off if each changeover is short, which is why heijunka and SMED are taught together.
- What is a heijunka box?
- A heijunka box is a board with a row for each product and a column for each pitch. A material handler releases one column of kanban cards every pitch. That paces the line in a level mix at takt, instead of sending a big batch order to the floor at once.