Estimation Techniques in Agile
T-Shirt Sizing method
T-shirt sizing is a form of relative estimation. This is an alternative to the more traditional, numerical story points estimation technique. It can be used as a high-level project estimation and capacity planning tool that can help track how much time or effort an initiative will take.
If you wish to use t-shirt sizing method for high-level project estimation, you can even custom create an estimator based on historical organizational data, domain, technology, team distribution, team’s average experience and skill level, and other metaphors.
When used for estimation User Stories, t-shirt sizing method can also be useful especially if you are working with a new team, or if the team is totally new to Scrum, or when trying to move away from estimating in hours. But later down the line you can remove the old T-shirt sizes and could move to estimating Product Backlog items using Story points.
T-shirt sizing as the name suggests is simply estimating with sizes similar to what you would find on a T-shirts’ label from Extra Small (XS) through to Extra Large (XL)… you can even keep going up to XXL, XXXL, etc. until it gets too dinosaur size shirt!
A t-shirt size of any item can represent it’s scope, effort, complexity, work hours, time estimates—or all of the above.
Sometimes teams find themselves over analyzing when trying to use Story Points. Thus by removing the implied precision of a numerical scores, the team is free to think in a more abstract way.
T-Shirt Sizing method is a quick way to estimate the size of any Epic, features or User Story (sometime for high level estimation purpose), as it can be achieved with a series of yes/no questions.
① We hold up story A and ask “Is story A double the size of story Z” (with story Z being our yardstick), if the answer is yes,
② we then ask the question “Is it more than double the size of story Z”, if the answer is also yes, we then
③ ask “Is it four times the size of story Z”, if the answer is no, we then mark the story as a “large” and move on.
The process:
❶ All the team member use their initial gut feeling and not to over think it.
❷ If there are some wildly different estimations coming from different team members, for example one says “small” the other says “large” the we should ask each member to explain the reasons for their estimation until the team reaches a consensus.
❸ you assign each epic, feature or user story a t-shirt size—from Extra Small to XXL—to represent the relative effort required to complete that task.
Pros
- T-shirt sizing is effective for its speed and ease-of-use when you still don’t have much of the information yet.
Cons
- Many of the tools out there for managing and measuring Scrum delivery base their reporting on story points or hours, which makes them ideally suited for additive ways of estimating and measuring.
- Unlike Story points, which can be added up, it’s tricky to review how much work is done or remaining.
- If not impossible, it’s difficult to measure velocity using t-shirt sizing method
- It’s harder to differentiate a precise difference between any of the two measurement criteria let say Small and Medium.
