What is Queue Time and How Does It Affect Manufacturing Lead Time?

What is Queue Time?

Queue Time is the time a job spends waiting before the next operation can begin.

The product is not being processed during this period it is simply waiting.

In simple terms

Manufacturing time can include:

Processing Time + Waiting Time + Movement Time + Inspection Time

A product may require only 30 minutes of actual processing but spend several hours waiting between operations.

Simple Example

A component requires:

• Cutting → 20 min
• Waiting → 90 min
• Drilling → 15 min
• Waiting → 120 min
• Assembly → 25 min

Actual processing time = 60 minutes

Total elapsed time = 270 minutes

So the product spends much more time waiting than being processed.

Why It Matters

Excessive queue time can create:

• Longer lead time
• Higher WIP
• Delayed deliveries
• Congestion between processes
• Poor flow
• Hidden capacity losses

Important Insight

When a production process is slow, the problem may not always be slow machines.

The machines may be working efficiently while products spend most of their time waiting for the next available resource.

How to Reduce Queue Time

1️⃣ Measure waiting time between operations.

2️⃣ Identify where WIP accumulates.

3️⃣ Compare process capacity between operations.

4️⃣ Check machine and manpower availability.

5️⃣ Improve production sequencing.

6️⃣ Reduce bottlenecks and unnecessary batch sizes.

7️⃣ Monitor waiting time after improvements.

Benefits

• Shorter production lead time
• Lower WIP
• Better production flow
• Faster response to customer demand
• Less shop-floor congestion
• Improved delivery performance

Practical Insight

If a product is being processed for 1 hour but takes 5 hours to travel through the factory, improving only processing time may have limited impact.

Sometimes the biggest opportunity is not:

“How can we process faster?”

but:

“Why is the product waiting so long?”