Lean Six Sigma Academy

Here’s the situation… the cycle time to produce one unit in our widget making factory is 300 seconds and the takt time for this product is 50 seconds per piece. In other words, in order to satisfy customer demand we need to produce a finish unit every 50 seconds.

How Many People?

OK, this is straight forward enough… but the next question is how many people do we need in the cell? One of the team members remembers hearing about some formula that looked at the ratio of cycle time to takt time to come up with the, so-called, optimal crew size.

Well, by taking 300 seconds (cycle time to produce one part) over 50 seconds (takt time) the team figured they needed 6 people in the cell. Is this correct?

Not So Fast

Well, as Lee Corso often says… “Not so fast my friends.” You see in order to accurately determine the optimal crew size the team needs a little more information.

Instead of stating the cycle time is 300 seconds, the team must first understand how much of that 300 seconds is “manual” cycle time – or the time an operator is actually needed – and how much is “automatic” cycle time – or the time the operator is technically not needed (such as when they hit the start button and commence reading their newspaper).

The Real Calculation

Now then… back to our widget factory. After some quick time studies the team learned that the manual cycle time is 100 seconds and the automatic cycle time is 200 seconds.

So, when they divided the sum of the manual cycle time – 100 seconds – by the takt time – 50 seconds – the optimal crew size came to 2 people (instead of 6 when the total cycle time was used).

Moral of the Story

So, the moral of the story is to calculate the optimal crew size of a work area by dividing the sum of manual cycle time by takt time. Of course, at this point the fun has just begun as the team must now determine what those 2 people will actually do! But let’s save that for another discussion.

Is this how you calculate optimal crew size in your organization?

1. Calculating Optimal Crew Size in Mixed Model Cells
2. How metrics like OEE often dictate behavior
3. Let’s Create a Future State Value Stream Map!
4. Lean Problem Solving
5. Standard Work