Formula for Six Sigma means how to calculate the sigma level of any process, from the six sigma perspective. In other words, formula for six sigma also means what is the current performance level of defects versus yield e.g. 10% defects and 90% yield….
Formula for Six sigma is also called ‘Z score’ in Six sigma science, which is the same thing, so with the help of this formula, we come to know whether our process is at 1 sigma level, 2 sigma level or 5 or 6 sigma level. And if we check the sigma accuracy table, we will know that how many defects, the process may be producing.
Formula for six sigma has to determine first the upper specification limits and lower specification limits as defined by the customers e.g. The acceptable weight in the army selection may be between 50 to 70 kgs. Now these are lower and upper specification limits. These are also called tolerance limits.
Formula for six sigma will be defined as follows:
Z Score = USL – LSL / Standard Deviation
If SD = 16
Z Score = 70-50 / 16 = 20 /16 = 1.25 sigma level
According to the sigma table; 1 sigma is 31% yield or 691500 defects per million opportunities, and 2 sigma is 69% yield or 308500 defects.
So you can now assess that since calculated sigma as per the formula for six sigma is 1.25 – yield will be slightly more than 31% and far less than 69% .
With this, you will get the sigma score and you can easily get to know immediately, how far you are from six sigma level performance.
Formula for six sigma is very simple and handy tool for anyone talking to any business. Even from the very early stages, with few questions and answers and with few data, any six sigma consultant can calculate the Z score or Sigma level and can fairly determine how much the scope for work for six sigma projects is.
These tolerance limits – upper and lower specification limits are very important to be captured correctly. Normally there should be defined USL & LSL in the company, but if these are not present, then there is more work first to be done in order to fine tune the tolerances.
Defining the correct USL & LSL is science as well as art. Much of the work of Six Sigma rests on these tolerance limits. If captured wrongly, the whole six sigma project can be jeopardized.
Formula for Six Sigma is simple yet at the same time very powerful and should be used often to get to know the current state of affairs in any business unit or process output.