As we understand, it doesn’t make sense to map story points with time just because it will be like comparing apples with oranges. Briefly following problems happen if we map story points with time:

• During the planning-poker exercise, the focus of the conflict tends to be the difference in time estimates among multiple developers instead of focusing around improving their shared understanding of the PBI through poker exercise.
• It becomes difficult to know how much work the team is finishing in each sprint as size of the work doesn’t get measured through such estimation, but the time does.

Some teams may be okay with these problems and still may want to get ahead with mapping a story point with time. However some teams may want to fix it.

In my experience, the teams which are already mapping a story point with time, for them it becomes difficult to unlearn this mapping even if the team desires to do so. 

At the same time, for teams which begin with a fair understanding that story points are all about size, complexity and uncertainty/risk, a question eventually comes around the mapping between a story point and time.

In one of these teams, instead of story points, we began with the idea of T-shirt size based relative estimation.

Rather than using numbers in the fibonacci series, here items are classified into t-shirt sizes: XS, S, M, L, XL.

Surprisingly everybody got the idea without any problems and with ease just because T-shirt sizing is all about size and not about time. The facilitator may ask team if the PBI is smaller or bigger than the baseline. If it’s bigger it moves to other T-shirt size bucket

These T-shirt sizes can further be mapped with story points. So XS becomes 1-2, S becomes 3, M becomes 5, L becomes 13 and XL becomes 20. Anything beyond, should be broken down further.

Let’s say a team planned for 2 XS, 2 S, 2 M and 1 L story. The number of story points they planned for the sprint is 2*1 + 2*3 + 2*5 + 1*8 = 26 story points, which then can be used for velocity trends.

I found it helpful to use T-shirt sizing instead of numbers as everyone in the team seems to get the message clearly.