T-shirt sizing has become a popular method for estimating in agile projects. So, In this video, I answer the question, what is T-shirt Sizing?
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T-shirt sizing is a simple and popular way to estimate the relative scales of different pieces of work. The method is usually used in agile projects and applied to User Stories.
The estimates are rough and ready, and give a first indication of the scale of work. They are less precise than full estimates or even other agile approaches, like Planning Poker, for example.
Typical T-shirt Sizes
Typically, we assign a T-shirt size to each item of work. Different users have different sizes, but a common approach might use sizes:
- Extra Small (XS)
- Small (S)
- Medium (M)
- Large (L)
- Extra Large (XL)
- Extra Extra Large (XXL)
Good Practice in T-shirt Sizing
In general, the more different sizes you use, the more variation you will get in how people interpret the terms. So, S, M, and L are the core sizes and you would be wise to resist the temptation to add too many more.
It is good practice to work through a few ‘type’ examples first, which you can use to establish a consensus of what, say, S, M, and L look like.
Interpreting T-shirt Sizes
There are different ways that teams can interpret the sizes.
But they often use Fibonacci numbers in the same way as Planning Poker, so, perhaps, in units of work:
- XS – 1
- S – 2
- M – 3
- L – 5
- XL – 8
- XXL – 13
Estimating from Iterations
Maybe the team will relate them to the number of iterations, or sprints, they will need, to develop the functionality:
- XS < 1
- S = 1
- M = 2-4
- L = 4-8
- L = 8+
The T-shirt Sizing Process
- Agree on your sizes and their definitions, and then make your T-shirt size cards
- The Product Owner explains the user story that needs an estimate. The development team asks questions to gain the understanding they need.
- Each developer gives the user story a t-shirt size.
- All developers raise their cards simultaneously.
- The development team discusses the differences and the product owner offers further clarification, if necessary.
- The team repeats Steps 3-5 until they agree on the size.
The Benefits of T-shirt Sizing
- Forcing the estimate into a small, fixed set of sizes means the process is informal and quick.
- It is very effective for getting an idea of what tasks in your backlog are similar sizes. This is sometimes called ‘affinity mapping’.
- Popular and fun.
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