12.4. T-Shirt Sizing

Nontechnical stakeholders often want (and need) to make decisions about project scope during the wide part of the Cone of Uncertainty. A good estimator will refuse to provide highly precise estimates while the project is still in the wide part of the Cone. Sales and marketing staff will say, “How can I know whether I want that feature if I don’t know how much it costs?” And a good estimator will say, “I can’t tell you what it will cost until we’ve done more detailed requirements work.” It would appear that the two groups are at an impasse.

This impasse can be broken by realizing that the goal of software estimation is not pinpoint accuracy but estimates that are accurate enough to support effective project control. In this case, nontechnical stakeholders are typically not asking for an estimate in staff hours. They are asking whether a specific feature is a mouse, rabbit, dog, or elephant. This observation leads to a very useful estimation approach called t-shirt sizing.