If your team is not experienced in estimating in story points — try estimating in T-shirt sizes! =)
Working in agile team I found at the beginning it is quite difficult for some people to switch from estimating in man-days to estimating in story points. The main complexity is to understand two things:
- story points express the size, not duration;
- and the size is relative, not absolute.
If you notice, your team-mates say "story points", but they mean/discuss/refer to man-days/man-hours — it is time to give a try the T-shirt sizes. The technique is to abstract the numbers and instead use the terms like Small, Medium, Large, eXtra Large. As you can see the T-shirt sizes better correspond to estimation in relative size.
After such estimation session you can convert the sizes back to numbers and send to the business. Hope it helps.