Are you looking for direct numbers? If so, I think that varies by person. I have read that it is about 150% by time. That is, if you are on the trainer (or spinbike) for an hour, that it is about equivalent to a 1 1/2 hour bike ride. Of course, depending upon how hard you ride that number may differ.

Due to really lousy weather up here in the snowbound north, I can state that the 150% adjustment is about right. During the week this winter, our longest time indoors would be about 1 1/2 hours. When we finally got outdoors this spring, a ride of a little over 2 hours was painless. No problems. When we pushed it to 3 hours, we had that "oh, we did a long ride" feeling.