calories burned spin class
It depends on how hard you're working, how much you weigh (and how much lean mass you have). I work near an 80% heart rate for most of my Spinning classes, and I only burn around 400-600 calories in an hour, sometimes less. There are a lot of factors at play. But a good HRM is one of the best ways to estimate how much you really burn in Spinning or in any activity for that matter.