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# Three Point Estimate Formulas ## Quick Reference on Three Point Estimate

I have written a series of articles on Three Point Estimate and related concepts. Before reading this, you should look at my first article of the series. I have explained the basic concept of Three Point Estimate in my first article. I have also explained that PERT is not synonymous with Three Point Estimate in that article.

In this article I have written all of the Three Point Estimate formulas and related concepts at one place. I have also added few more things that were not explained earlier. The explanation of formulas and some examples can be found in my other articles on Three Point Estimate.  You can bookmark this article for ready reference.

Expected Value or Mean for Triangular Distribution

E =(O+P+M)/3

Standard Deviation for Triangular Distribution

σ =SQRT [{SQR(P – O) + (M – P)(M – O)}/18]

Expected Value or Mean for Beta Distribution

E =(O+P+4×M)/6

Standard Deviation for Beta Distribution

σ = (P – O)/6

Range of Estimate

E ± (n * σ)

Variance of an Activity

Var = SQR(σ)

Variance of a Schedule Network Path

Var_Path = ∑(Var)

Standard Deviation of a Schedule Network Path

σ_Path = SQRT(Var_Path)

In the above formulas O, P and M are Optimistic, Pessimistic and Most Likely values respectively. ‘n’ is sigma level which determines the Probability  or Confidence Level.

• If n=1 then Probability is 68.27%
• If n=2 then Probability is 95.45%
• If n=3 then Probability is 99.73%
• If n=4 then Probability is 99.994%
• If n=5 then Probability is 99.99994%
• If n=6 then Probability is 99.999999%