You can look at the number of clicks/views generated by each. I read once that Ashton Kutcher tweeted about a service which reported the number of visits from

You can look at the number of clicks/views generated by each. I read once that Ashton Kutcher tweeted about a service which reported the number of visits from his tweet equated to about 3% of his follower base at the time. He probably gets a lot of RTs, but we can use that as an estimate. For RSS subscribers, I've seen roughly a 25% "reach" via Feedburner. So, that would mean 1 RSS subscriber = 8 twitter followers. That's assuming you have all legitimate, natural twitter followers and haven't tried to inflate your twitter count. It probably varies greatly by the types of users and quality of content.