Big/Uncertain/Small is an agile estimation method where the items to be estimated are placed by the group in any of these categories – big, uncertain and small. Teams discuss a few items together and then uses divide-and-conquer to estimate the remaining items. Big/Uncertain/Small is just like the Bucket System. In the divide-and-conquer step, you allocate the remaining items to all members of the team. Every member puts items on the scale without discussing it with other team members. If someone has an item that he doesn’t really understand, that item can be given to someone else.
Benefits of Big/Uncertain/Small
Big/Uncertain/Small is designed to be collaborative. This means that everyone in the team contributes roughly equally. The results cannot be traced to one person, so this agile estimation method promotes group accountability. Even if someone makes the wrong estimate, that person cannot be determined. No one will know what his estimation was. Blaming someone in the team when something goes wrong is avoided. Since the method is collaborative, all the right people participate in the estimation process. No team member can give any excuse and escape from the responsibility of taking part in the process of estimation. Everyone in the team needs to work together.
This agile estimation method also takes advantage of people’s ability to compare things and helps teams avoid comparing items to abstract concepts. As such, the estimation process is simpler and can be completed much faster. Teams don’t need to use old-fashioned techniques that will take so much of their time. With Big/Uncertain/Small, they can save time and focus more on collaboration.
Big/Uncertain/Small is similar to TFB / NFC / 1 (Sprint). However, TFB / NFC / 1 (Sprint) includes a specific size and that’s 1 Sprint. The categories in TFB / NFC / 1 (Sprint) are “1” Sprint, Too F-ing Big and No F-ing Clue.
There are other agile estimation methods that teams can use aside from Big/Uncertain/Small. One of these is Affinity Mapping where items are assembled by similarity. This similarity is usually a physical activity and needs a small number of items. The groups are linked to numerical estimates if preferred.
Another agile estimation method is T-Shirt Sizes. Items are grouped into t-shirt sizes – S, XS, M, L and XL. If required, the sizes can be given numerical values once the estimation is completed. This method can be used with a large number of items. The decision about the size is usually based on open, collective discussion. By using an agile workflow, the team can estimate new work more effectively.
As they face new stories, they will have a more precise sense of how they should treat each user story. They will also know the amount of effort they need to spend on each story to complete it. A group that has been working together for some time can estimate new stories much better. Agile estimation methods can get all members of the team involved in productive estimation regardless of their experience level with agile methods.

— Slimane Zouggari