I am a Scrum Master of a team with 12 members. I know that the size of the team is large at this point, but as we grow further we will divide the team into multiple Scrum Teams. Our estimations for the User Stories are based on Story Points. For the tasks within a User Story we are estimating in hours. Based on the first 6 Sprints we were able to establish a team Velocity. 

We did not have any issues in taking the User Stories, because we knew how many User Stories we could take for the Sprint based on our Velocity. When a couple of team members went on a planned leave, we were unable to estimate the number of Story Points we had to commit. Since we are not calculating Velocity per team member, we are unable to estimate how many Story Points we should take for the next Sprint. So, my question is **how do we calculate the story points we can commit to the sprint when some of the team members are on a leave**?

My second question is we are calculating the number of hours each team member is available for the sprint. As we should not directly map Story Points to hours, we are not seeing the value of calculating the number of hours for each team member during the Sprint Planning Meeting. **How do we establish a relation between hours and story points?**