Sigma Performance Levels – One to Six Sigma

When learning about Six Sigma, it may help to consider these charts, which detail how sigma level relates to defects per million opportunities (DPMO), and some real-world examples.

Sigma Performance Table

Sigma Performance Levels – One to Six Sigma
Sigma Level Defects (or Errors) Per Million Opportunities (DPMO) Yield (or Produced or Delivered) Correctly (%)
1 691,462 30.85
2 308,538 69.146
3 66,807 93.319
4 6,210 99.379
5 233 99.9767
6 3.4 99.9997

What Would Sigma Values Look Like In The Real World?

It’s one thing to see the numbers and it’s a whole other thing to see how it would apply to your daily life.

Real-world Performance Levels
Situation or Example In 1 Sigma World In 3 Sigma World In 6 Sigma World
Pieces of your mail lost per year [assuming 1,600 opportunities per year] 1,106 107 Less than 1
Number of aircraft takeoff or landing incidents [assuming one takeoff and landing per flight, round trip] 25 times per 10 flights 24 times per 100 flights 12 times per million flights
Number of empty coffee pots at work (who didn’t fill the coffee pot again?) [assuming 680 opportunities per year] 470 45 Less than 1
Number of telephone disconnections [assuming 7,000 talk minutes] 4,839 467 0.02
Erroneous business orders [assuming 250,000 opportunities per year] 172,924 16,694 0.9
Electricity outage [assuming 30 day month = 720 hours] 500 hours 45 hours 9 minutes

In the United States alone if the sigma level were between 3 and 4, there would be 50 newborn babies dropped per day and 5,000 incorrect surgical procedures per week.

Not all opportunities and defects are created equal. I think all flight passengers would agree that a flight delay is less worrisome than a flight incident on landing.

Comments 21

  1. vijayarajaa

    why do you mean 3.4 ppm as six Sigma

  2. vijayarajaa

    why can,t we say that seven sigma or eight sigma instead of six sigma? or explanation of Six?

  3. Bharat joshi

    Six sigma 3.4 ppm mean 3.4 defect per million opportunity.

    It means 99.99966 % data falls withing specification. so that 100-99.99966=0.00034% = 3.4 ppm

  4. gascan911

    no wrong !, 3.4 doesn’t mean 0.00034% defects or 99.99966% good
    6 means 99.9997 % good
    and there are six [6] sigma levels not 3.

    calculated as
    [ defect units / (no. of oppertunities * no. of units) ] * 1,000,000

  5. fargato

    But U know that in calculating of actual capability metrics the normal distribution is from -3s to +3s (centered process). In there are about 99,….% probability of execute products is six sigma level quality. So, from -3s to +3s there is 6 sigma. I must say that in banking exist 7 sigma level.

  6. Ray-Ciocon

    Thank you for your comments. I see that Six Sigma represents a measurement for the number of defects in a near perfect level of performance in anything we can do.

  7. VM

    Defect counts are like random variables representing deviation from mean. They follow bell curve (normal distribution) and have a mean (mu) and a standard deviation (sigma) like any other random distribution.

    By counting defects per million you can judge the quality maturity of your process in units of one two three or six times the standard deviation (sigma).

    1 2 3 6 sigma = 68% 95% 99.7% and 99.9999998% (percentage of total area under normal bell curve)

  8. Prathamesh

    How you calculate 1sigma=690,000, 2sigma= 390,538 etc.? Is there any formula?

  9. Rabishankar

    So Beautifully n simply expressed – so easy for commoners – Gr8

  10. Bonkers

    Are you sure about those numbers? 67% failure rate at 1-sigma?
    the tails should be 16% each side at 1-sigma
    and 0.6ppm at 5-sigma, not 233ppm

    I get these:
    N NORM.DIST(N,0,1,TRUE) 1-this 2*1e6 x that
    1 0.841344746 0.158655254 317310.5079
    2 0.977249868 0.022750132 45500.2639
    3 0.998650102 0.001349898 2699.796063
    4 0.999968329 3.16712E-05 63.34248367
    5 0.999999713 2.86652E-07 0.573303144
    6 0.999999999 9.86588E-10 0.001973175

    • EsbenJensen


      The misunderstanding is based n the fact that a 1.5 sigma long term shift is normally applied when talking about six sigma. 3.4ppm defects equals 4.5 sigma without the long term shift.

      Hope this helps

  11. Marylou Karkow

    MD said I had 2 S.D. chance of death after 5 Years ( 1985); 3 SD (99%) in 10 years (Y2K). As I am still living, how many SD’s am I now?

  12. Junior Faka

    Perfect explanation

  13. Ravneet


    Why six sigma is calculated in million only and not in billions?

  14. shankha shubhra goswami

    everything is ok but the main question is why 3.4defects is rated as 6sigma? why not 5defects or some other value? how the 3.4 value is coming and why it is rated as 6sigma? pls help me. i will be grateful to you. and also explain how to calculate sigma rating from no.of defects

  15. shankha shubhra goswami

    suppose there are 50,000 inspected parts and among these 150 parts are found to be defective. so what is the sigma rating for these and how to calculate it? pls help me.

  16. Lathesh mk

    Hello Kristine,

    Where do we get “Sigma Performance Levels – One to Six Sigma”

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