I have read it that all the Scrum Teams working on the same product can have different Sprint length. for instance, some teams can have a sprint length of 2 weeks and some can have length of 3 weeks. Can anybody help me understand how can then be velocity calculated in the case where sprint length varies for a different team? To my understanding, Team size and length should be the same for calculating average velocity. Please advise if I am following anything incorrectly.
What reason would you have for calculating an average velocity that's an aggregate of multiple teams?
Outside of velocity, if these teams are working from the same product backlog you may want to consider any challenges in delivering a working integrated increment each Sprint if each team has varying Sprint lengths.
Why would you even consider calculating an average velocity across teams? Velocity is team specific and only benefits the team that is actually creating the velocity. And what data points are you using for the calculation you are planning to do? Since each team estimates and refines stories differently neither of those data points work for cross team comparisons.