Well I would say about 400 to 500 depends what speed your going at
My bike computer reckons I do over 1000 Calories in that time. But I am not convinced
Theres no possible way only 30 minutes of bike riding burns 400-500 calories. For a person weighing about 130 pounds you burn about 350 calories per HOUR. But it all depends on what speed you were going and how hard your heart was working.
I just did that like five minutes ago-I was searching that on google and I clicked on this link. I read that you burn approximatly 200-500 calories (more on the 200 side) I hope that helps:)