I don't know any methods of estimating calories consumed. I recently started using a Garmin Edge 200 bike computer. They go for about $100. It asks me my weight and height. I don't know why height is relevant. It gives me calorie consumption, but I have no idea if it's accurate. I haven't paid attention to calories, at least not yet. I manage to regulate my weight well enough.

See this ride I took on November 19. It says I burned 1,190 calories. I went very slowly because I didn't know the route, and traffic was very hairy. There were also extremely strong winds that day. I weigh 170 lbs (77kg), and my bike is another 30 or 35. I'm 5'9-1/2" (176 cm) tall, if that matters at all.