Understanding the capability of your process is essential to choosing the correct improvement strategy.

Our process capability calculator for Cpk Upper (the capability measure generally of most interest to service and transactional businesses) makes calculating your process capability level simple and quick.

You need four pieces of information to calculate Cpk upper:

1. Your customer's requirement, which is usually expressed as the Service Level Agreement (S.L.A.) in service and transactional organisations. For example, no more than 16 minutes to respond to a customer query.
2. The mean value of your process' current performace. For example on average we respond in 15.9 minutes to a query.
3. The mean range value of your process' current performance. For example 0.034 minutes. The way you calculate this mean range value will depend on whether you are using an Individuals and Moving Range or an X Bar R control chart to measure your process.
4. The sample size you are using to measure your process. If you are using an Individuals and Moving Range chart to measure your process this will be 2. If you are using an X Bar R chart to measure your process, this will most likely be 2, 3, 4 or 5. 

The calculator defaults to a set of values initially, and you simply change these to suit your needs. 

If the calculated Cpk value is <1, it means that some of the output from your process is guaranteed to fail to meet customer requirements. As the Cpk value gets increasingly lower than 1, it means that increasingly more of the output from your process will fail to meet customer requirements.

If the calculated Cpk value is 1, it means that provided your process does not drift and it behaves completely 'normally' (which is, in practice, relatively unlikely) then almost all of the output from the process will meet customer requirements. At a Cpk of 1 your process will be running at around 3 sigma. Cpk 1 is the minimum target for your process, although Cpk 1.33 is a practical minimum target for a customer-focused business.

If the calculated Cpk value is 2, it means that your process will hardly ever fail to meet customer requirements. At a Cpk of 2 your process will be running at around 6 sigma (depending on how you calculate sigma values) and should produce less than 4 defects in a million outputs. 

If the calculated Cpk value is > 2 then you are doing very, very well if you are a service or transactional organisation. Go celebrate!

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