# Six Sigma Calculation

Six Sigma – iSixSigma Forums Old Forums General Six Sigma Calculation

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• #43944

Debabrata Biswas
Participant

Hi Everyone,
I have a problem to calculate the Sigma value in MS-Excel. I just want to know the basic function of “NORMSINV”. I mean how this finction actually perform? what it indicate? can anybody explain me the step by step calculation of “NORMSINV”!!!

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#140056

Brit
Participant

The NORMSINV(1-((total defects)/(total opportunities)))+1.5 provides the Z value or the count of standard deviations (i.e., sigma level).  The 1.5 added to the formula accounts for the long term sigma shift.

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#140087

Debabrata Biswas
Participant

sir,
thanks for your discussion about NORMSINV.but is there any other process to calculate Sigma Value in Excell

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#140121

Ropp
Participant

To calculate sigma: use the fx (function icon) and select “std dev”.  You may need to look around a bit to find it.  Once you select std dev (sigma) select your data range, and hit enter.  Sigma will automatically calculate for you.  Once you have “sigma” you can calculate your upper and lower process range by typing the following formulas in appropriate cells in your spread sheet.
=average+(3*std dev)  std dev – select the cell just used to create sigma
=average-(3*std dev)
This will give you your current process range and hopefully both numbers will be within your process USL & LSL.
This information can also be used to estimate and create tolerance ranges during initial design experiments.

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#140125

Brit
Participant

The answer you got from Dave was how to find the standard deviation (greek symbol sigma). I don’t think this is what you were asking about.
Use NORMSINV to find the sigma level (or number of standard deviations between average and upper or lower specification). I know of no other excel function that can be used to determine sigma level, but someon else might.

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