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Lean ManufacturingKanban
Level
Volume & Mix
Mura
The Enemy: Unevenness
Daily
Build Every Product
SMED
Enables Leveling

What Is Heijunka?

Heijunka (hay-JUNE-kah) is the Japanese term for production leveling — distributing production volume and product mix evenly over time. Instead of building all of Product A on Monday and all of Product B on Tuesday, heijunka spreads both products across every day (or every shift, or every hour).

Heijunka attacks mura (unevenness), which Toyota considers the root cause of both muri (overburden) and muda (waste). When demand is lumpy, everything downstream suffers: overtime one week, idle time the next; inventory spikes then shortages; suppliers whipsawed by erratic orders.

Two Types of Leveling

TypeWhat It LevelsExample
Volume LevelingTotal quantity per periodInstead of 800 Monday / 200 Tuesday / 600 Wednesday, produce 500 every day
Mix LevelingProduct variety per periodInstead of AAAA-BBBB-CCCC, produce ABCABC — every product every interval

Volume leveling is easier and should come first. Mix leveling is harder (requires short changeovers) but delivers the biggest flow and inventory benefits.

Why Batch Production Creates Chaos

❌ Batched Schedule
  • Monday: 2,000 units of Product A
  • Tuesday-Wednesday: 1,500 units of Product B
  • Thursday: 800 units of Product C
  • Friday: Catch-up / overtime for missed production
  • Result: Huge WIP, long lead times, overtime every Friday, suppliers cannot keep up, finished goods pile up then run out
✅ Level Schedule
  • Every day: 400 A, 300 B, 160 C
  • Repeated pattern: AABABCAABABC...
  • Same total weekly volume, evenly spread
  • Result: Stable WIP, short lead times, no overtime spikes, suppliers get steady demand, finished goods replenished daily

The Heijunka Box

The heijunka box is a physical scheduling device — a grid of slots where rows represent products and columns represent time intervals. Production cards (kanban) are placed in slots to create the leveled sequence. The material handler pulls cards from left to right, delivering them to the line in the planned sequence.

7:007:308:008:309:009:30
Product A🟢🟢🟢
Product B🟢🟢🟢
Product C🟢

The Heijunka Box Is a Pacemaker

The heijunka box sets the rhythm for the entire value stream. Upstream processes produce to replenish what the pacemaker process consumed. Downstream processes receive a steady, predictable flow. It replaces the MRP-driven batch schedule with a visual, pull-based rhythm.

Prerequisites for Heijunka

Leveling does not work without these foundations in place:

Short changeoversIf changing from Product A to B takes 2 hours, you cannot change 6 times per day. SMED is the enabler of heijunka — reduce changeovers to single digits before attempting full mix leveling.
Reliable equipmentLevel scheduling assumes the line will run when scheduled. Frequent breakdowns destroy the leveled plan. TPM is essential.
Stable qualityIf scrap rates spike unpredictably, you cannot produce the right quantity of each product. Jidoka and poka-yoke reduce quality disruptions.
Flexible workforceOperators may need to run different products each shift. Cross-training (TWI) and skill matrices make this possible.
Finished goods bufferDuring the transition from batch to level, you need a buffer of finished goods to absorb the difference between lumpy customer orders and level production. This buffer shrinks over time as lead times drop.

Implementing Heijunka

Start with volume levelingCalculate average daily demand for total volume. Smooth the weekly schedule so each day produces roughly the same total quantity. This is the quick win.
Reduce changeoversApply SMED to the pacemaker process. Target: changeover time shorter than the pitch (the time interval between product changes in the heijunka box).
Calculate the repeating patternBased on demand ratios, create a repeating production sequence. If demand is 3A:2B:1C, the pattern is AABABC. This repeats throughout the day.
Set up the heijunka boxBuild or buy a visual scheduling board. Load it daily with kanban cards in the leveled sequence. The water spider pulls cards and delivers to the line.
Measure and adjustTrack schedule adherence: did the line follow the leveled sequence? When disruptions force deviation, understand why and fix the root cause. Perfect adherence is the target.

Heijunka ≠ Ignoring Demand Variation

Heijunka does not mean producing the same thing every day regardless of demand. It means smoothing the demand signal over an appropriate period (week, day) and producing to that smoothed signal. Actual customer orders are still fulfilled from a small finished goods buffer. As your system matures, the buffer shrinks because lead times shrink.

🎯 Key Takeaway

Heijunka is the missing link between kanban (pull) and stable operations. Level production eliminates the peaks and valleys that cause overtime, excess inventory, and supplier chaos. Start with volume leveling (same total output daily), then build toward mix leveling as changeover times drop through SMED. The reward: shorter lead times, lower inventory, less overtime, and a calm, predictable operation.

Interactive Demo

Compare batch vs leveled production. See how heijunka reduces inventory peaks and smooths workflow.

⚡
Try It Yourself
Heijunka Production Leveling
▼
Toggle between batch and leveled production to see how leveling reduces inventory peaks. Arrange the heijunka box to visualize the mixed-model schedule.
20 units
2 units30 units
12 units
2 units30 units
8 units
2 units30 units
Heijunka Box — Weekly Schedule
DayS1S2S3S4S5S6S7S8S9S10
Day 1
A
A
A
A
A
A
A
A
A
A
Day 2
A
A
A
A
A
A
A
A
A
A
Day 3
B
B
B
B
B
B
B
B
B
B
Day 4
B
B
C
C
C
C
C
C
C
C
Day 5
Product A
Product B
Product C
Inventory Levels Over Time
0612Day 1Day 2Day 3Day 4Day 5
12 units
Max Inventory
7.9 units
Avg Inventory
40 units
Total Demand
BATCH
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Take this to a room

The running order

For schedulers and production managers. They should leave able to describe their current weekly pattern and the first levelling move they can make without any changeover work.

7 beats · 10 min
  1. 1

    Look at our own week

    Put last week's daily output on the board. Almost nobody's is flat.

    • Typical: 2,000 A on Monday, 1,500 B midweek, 800 C Thursday, catch-up Friday.
    • The result is overtime every Friday and finished goods that pile up then run out.
    • Suppliers see the same lumps and build their own buffers against us.

    Ask the room What did we build each day last week, and why that shape?

  2. 2

    Mura is the target

    Heijunka attacks unevenness. Not waste, not overburden - unevenness, which causes both.

    • Uneven volume causes overtime peaks and idle troughs.
    • Uneven mix causes changeover chaos and inventory swings.
    • Levelling is upstream of most of the firefighting we do.
  3. 3

    Two kinds of levelling

    Volume first, then mix. They are different problems and the first one is nearly free.

    • Volume: instead of 800 / 200 / 600, build 500 every day.
    • Mix: instead of AAAA-BBBB-CCCC, build ABCABC.
    • Volume levelling needs only scheduling. Mix levelling needs short changeovers.

    Ask the room Could we flatten total daily volume next week without touching changeovers?

  4. 4

    The pattern comes from the ratio

    You do not invent the sequence. Demand gives it to you.

    • Demand 3A : 2B : 1C gives the repeating pattern AABABC.
    • That pattern repeats all day, every day.
    • The heijunka box holds the cards in that sequence and paces the line.
  5. 5

    The box is a pacemaker

    It replaces the MRP batch schedule with a visual rhythm the whole stream can see.

    • Upstream produces to replenish what the pacemaker consumed.
    • Downstream receives a steady, predictable flow.
    • The water spider pulls the next card at the pitch interval.
  6. 6

    What has to be true first

    Four prerequisites, and the first is the one that stops most plants.

    • Changeovers shorter than the pitch - SMED is the enabler.
    • Reliable equipment, or the levelled plan is fiction.
    • Stable quality and cross-trained operators.
    • A finished-goods buffer during the transition, which shrinks as lead time drops.
  7. 7

    What we do next

    Level volume next week, then start SMED on the pacemaker.

    • Calculate average daily demand and flatten the weekly schedule to it.
    • Apply SMED to the pacemaker until changeover is under the pitch.
    • Build the repeating pattern from the demand ratio, then load the box.
    • Track schedule adherence and treat every deviation as a problem with a cause.

    Ask the room What is our pacemaker process, and what is its changeover time?

Related Guides

⏱️ SMED
Enable frequent changeovers
📅 Production Scheduling
Build the leveled schedule
📋 Kanban Systems
Pull-based replenishment