T-shirt sizes and story points

 In the previous blogs, you learned about T-shirt sizes and story points—the two most common units used to help teams estimate user stories in Agile projects. In this reading, we will explore the processes of estimating user stories in these units. 

As a recap, relative estimation means to compare the effort estimated for completing a backlog item to the effort estimated for another backlog item. Doing this instead of trying to determine exactly how long a task will take allows your comparisons and estimates to be more accurate relative to one another.

T-shirt sizes

At first, T-shirt sizes may seem like a somewhat unusual way to measure an item or user story. But when you think about assigning estimations to items based on sizes (e.g., XS, S, M, L, XL, XXL), it is actually very helpful and easy. Some of the benefits to using this technique are that it is quick, well understood by Agile experts, and a good introduction for teams who are just learning relative estimation.

So what does the process of assigning T-shirt sizes entail? There are several specific techniques a team can try, but each generally follows these steps. The team: 

• Agrees on the chosen scale and metrics to be used.

• Identifies at least one anchor backlog item. That item will be assigned a T-shirt size. Some teams will choose two anchor items—one at the top of the range and one at the bottom of the range.

• Sorts through the remaining backlog items and agrees on T-shirt sizes for each of them. 

Story points

Using story points as the estimate unit is a little more advanced than T-shirt sizes, but it is essentially the same concept. This method is good for experienced teams. When using story points, teams usually use the Fibonacci sequence. As a reminder, this sequence comes from adding the two previous numbers in the sequence together. For example, 1 + 2 = 3 and 2 + 3 = 5. The important thing to notice about this sequence is that, as the list continues on, the numbers spread further apart from each other. Because of this, story points provide more accuracy and specificity than T-shirt sizes. 

So what does the process of assigning story points entail? There are several specific techniques a team can try, but the basic steps are the same as with T-shirt sizes. The team: 

• Agrees on the permitted points values. Some teams cap the size at a certain number, like 21. Some teams decide to jump from 21 to 100 as the next larger value. This is a team decision.

• Identifies at least one anchor backlog item and agrees to assign it a points value. Some teams will choose two anchor items, one at the top of the range and one at the bottom of the range.

• Sorts through the remaining backlog items as a team, agrees on an estimate for each item, and captures it in the backlog management system. 

Best practices

Some best practices, regardless of the technique you use, include:

• Asking the Product Owner questions about the user story or item to ensure that there is enough information to estimate it.

• Discussing divergent estimates from various team members so that everyone has a chance to understand how to implement the item.

• Agreeing on the final T-shirt sizes or points value and capturing it in the system.

• If certain items fall into the larger T-shirt size or story points value range, discussing whether it makes sense to break them down into smaller pieces before moving on.

Key takeaway

Either of these effort estimation units are effective at estimating your items and user stories. As a team, it is important to spend the appropriate amount of time deciding which is best for you. If you are a less experienced team, try starting out with T-shirt sizes, but more advanced teams should feel free to use either method.

Would love to know your thoughts around this topic, please comment below.