Understanding Flow Efficiency in Kanban Systems

In any workflow, time is spent in two ways: either actively working on a task or waiting for something. Flow efficiency is a key metric in Kanban that measures the ratio between active work time and total lead time. Understanding and optimizing this metric can dramatically improve your productivity and delivery speed.

What is Flow Efficiency?

Flow efficiency is calculated with a simple formula:

Flow Efficiency = (Active Work Time ÷ Total Lead Time) × 100%

Where:

• Active Work Time: Time spent actually working on a task
• Total Lead Time: Calendar time from start to finish, including both active work and waiting time

For example, if a task takes 10 calendar days to complete, but only 2 days of actual work was performed on it, the flow efficiency is: (2 ÷ 10) × 100% = 20%

Why Flow Efficiency Matters

In most organizations, flow efficiency is surprisingly low—typically between 15% and 30%. This means that for most tasks, 70-85% of the time is spent waiting rather than in active work!

Improving flow efficiency offers significant benefits:

• Faster delivery: Reducing wait time means completing work sooner
• Increased capacity: Higher efficiency means more throughput with the same resources
• Better predictability: More efficient processes lead to more consistent delivery
• Higher quality: Less waiting means fewer context switches and better focus
• Improved morale: People prefer adding value to waiting for things to happen

Measuring Flow Efficiency

To calculate flow efficiency accurately, you need to track:

Active Work Time

Record when tasks are actively being worked on. This can be done through:

• Time tracking tools
• Status updates on Kanban cards
• Work logs and activity records

Total Lead Time

Measure the calendar time from when work starts (enters your "In Progress" column) until it's completed (reaches "Done").

Creating Efficiency Metrics

With this data, you can calculate flow efficiency at multiple levels:

• Individual task efficiency
• Project efficiency
• Team efficiency
• System-wide efficiency

Common Causes of Low Flow Efficiency

Understanding what causes waiting time is crucial for improvement:

1. Handoffs

Each time work passes from one person or team to another, delays occur. The more handoffs in your process, the lower your flow efficiency.

2. Batching

When work is processed in batches rather than flowing continuously, items spend time waiting for the batch to be processed.

3. Dependencies

Tasks that depend on external factors (approvals, resources, other tasks) often experience significant waiting time.

4. Multitasking

When people work on multiple tasks simultaneously, each task progresses more slowly due to context switching and partial attention.

5. Unclear Priorities

Without clear prioritization, important work can wait while less valuable tasks move forward.

6. Process Bottlenecks

Constraints in the workflow create queues of waiting work.

7. Approval Processes

Review and approval steps often introduce substantial waiting periods.

Visualizing Flow Efficiency on Your Kanban Board

Make waiting visible on your board:

1. Waiting Columns

Add explicit "Waiting" columns between active work stages:

• Ready
• Development
• Waiting for QA
• QA Testing
• Waiting for Approval
• Deployment

2. Blocker Indicators

Use visual markers (red flags, stickers, or tags) to indicate when items are blocked or waiting.

3. Aging Cards

Implement an aging mechanism where cards change appearance (e.g., color fades) the longer they remain inactive.

4. Cumulative Flow Diagram

Use this chart to visualize the accumulation of work in different stages over time, making bottlenecks apparent.

Strategies to Improve Flow Efficiency

Once you understand your current flow efficiency, try these strategies to improve it:

1. Reduce Batch Sizes

Process smaller amounts of work at once:

• Break large tasks into smaller ones
• Release in smaller increments
• Review work more frequently in smaller chunks

2. Limit Work in Progress (WIP)

Lower WIP limits force completion of existing work before starting new items, reducing overall wait time.

3. Implement Pull Systems

Have downstream stages pull work when they're ready rather than having upstream stages push work when they're done.

4. Cross-Functional Teams

Reduce handoffs by having teams with all the skills needed to complete work from start to finish.

5. Standardize Work

Creating standard procedures reduces variability and waiting due to uncertainty.

6. Address Bottlenecks

Identify and resolve constraints in your workflow:

• Add capacity to bottleneck stages
• Reduce work that needs to flow through bottlenecks
• Create bypass lanes for certain types of work

7. Class of Service Policies

Implement different handling rules for different types of work:

• Expedite lanes for urgent items
• Standard lanes for normal work
• Intangible lanes for learning and improvement

Setting Flow Efficiency Targets

While 100% flow efficiency isn't realistic (some waiting is inevitable), you can set improvement targets:

• Starting point: Measure your current baseline (often 15-30%)
• Initial target: 40-50% flow efficiency is achievable for many teams
• Advanced target: 60-70% for highly optimized systems
• Context matters: Different work types may have different potential efficiencies

Implementing Flow Efficiency Measurement

Start tracking flow efficiency with these steps:

1. Track active time: Implement a way to record when tasks are being actively worked on
2. Measure lead time: Record start and end dates for all work items
3. Calculate baseline: Determine your current flow efficiency
4. Identify patterns: Look for types of work or process stages with particularly low efficiency
5. Target improvements: Implement changes focused on reducing wait time
6. Monitor trends: Track flow efficiency over time to ensure improvements stick

Beyond Basic Flow Efficiency

As you get comfortable with flow efficiency, consider these advanced concepts:

Value Stream Mapping

Create detailed maps of your entire workflow to identify all waiting points and non-value-adding activities.

Economic Cost of Delay

Calculate the financial impact of waiting time for different types of work to prioritize improvement efforts.

Little's Law

Understand the mathematical relationship between WIP, cycle time, and throughput to make data-driven process improvements.

By focusing on flow efficiency, you move beyond simply managing tasks to optimizing the entire system of work. The result is faster delivery, higher capacity, and a more satisfying work experience for everyone involved.