There are several common relative estimation methods when estimating user stories. T-shirt sizes is one of the most common units to help teams estimate user stories in Agile projects.  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. 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.