There are two recently introduced fields on Rally portfolio items; "Estimated Progress by Story Points" and "Estimated Progress by Story Count".
This article discusses the basic usage of these fields.
The values for the two fields are initially driven by the Preliminary Estimate field.
You can set the values for these in your workspace settings, under the Fields section for Portfolio Items.
When you choose a preliminary estimate value on a portfolio item, it populates those two fields with the initial values from the Preliminary Estimate field settings. For example, in the screenshot below we have selected M which corresponds with 5 points and 4 stories.
However, there is a high possibility that these initial values will need to be refined, and we can do so using the "Refined Estimate" and "Refined Work Item Count Estimate" fields.
In the screenshot below, we have updated the values to 7 points and 5 story count: