tags: #publish links: [[Estimation Techniques]] created: 2021-07-28 Wed --- # Three-point estimation https://en.wikipedia.org/wiki/Three-point_estimation https://www.projectmanagement.com/contentPages/wiki.cfm?ID=368763&thisPageURL=/wikis/368763/3-Points-Estimating#_=_ Useful when you have limited information, to obtain an idea of the likely probability distribution of the actual cost. Make three best-effort guesses based on prior experience: - **a**: *best-case* optimistic estimate - **m**: *most likely* estimate - **b**: *worst-case* pessimistic estimate Then combine them to produce an actual "expected" estimate, **E**: ## Variants ### Crude Estimate the three things then intuitively pick a final estimate. The process of thinking about best and worst cases helps broaden thinking. ### Beta / PERT / Probabilistic See [[PERT]] More weight is given to the **most likely** estimate, giving a normal distribution shape: `E = (a + 4m + b) / 6` `SD = (b − a) / 6` One can combine these task estimates to estimate overall project and likelihood of variance - see the Wikipedia page. ### Triangular / symmetric `E = (a + m + b) / 3`