Most Agile estimation techniques use relative units like story points or T-shirt sizes to estimate effort. This means that we don’t try to estimate hours, dollars, or days directly. This type of estimation takes advantage of the human capacity to compare things to each other and avoids the human difficulty in comparing abstract concepts like money or time. Agile estimation techniques are collaborative because the room is always smarter than the smartest person in the room. When beginning an estimation session, make sure all appropriate people (A.K.A. the people who will be doing the work) are included in the process. Remember, the whole Scrum team participates in estimating effort of product backlog items. Collaborative techniques are also designed so that it is impossible to blame someone for an incorrect estimate because there is no way to trace who estimated what. This is important because the only way to get better at estimating, is to practice estimating.
Ordering Protocol (Relative Mass Valuation)
You have done this a thousand times already since childhood. Just start lining printed backlog items up in order from smallest to largest, squeezing things in between as needed until everything is in order. You may have some dense areas when you came across items that seemed about the same size and you piled them together. Now imagine laying a number line next to your line of backlog items. Your number line might go from 1-100, or it might use something like a Fibonacci sequence. Now, simply transfer the numbers to the backlog items, and “ta-da” your backlog has been estimated! This method works well for a team new to estimating who has a large number of items to estimate. There is a very similar method called the Bucket System that might also be a great place to start for your team, or for working with stakeholders to determine relative value of features.
T-Shirt Sizes
Remember the cone of uncertainty? T-Shirt sizes are a popular way of estimating work that is far from certain. It does make roadmapping difficult however, and as the cone of uncertainty narrows, I recommend moving to story points.
Planning Poker
You can “play” planning poker to estimate story points for your backlog items with printed cards, or virtual cards. Watch this quick video to get a quick lesson on how it works.