Calories burned depends on a number of factors -- your age, weight, speed, level of exertion. I would recommend a free website/app called loseit.com

I have used LoseIt to successful drop 30+ lbs. and maintain my target weight for past couple of years. You have to track both calories eaten and burned through exercise to make best use of the site/app. The LoseIt program automatically adjusts your calorie burn from exercise to your weight. For instance, as you lose weight, you burn fewer calories from a given amount of exercise because your body needs less energy to perform a given task at a lower weight. It also adjusts your calorie burn to your level of exertion -- which is approximated by your average speed. For example, I burn about 725 calories/hour cycling in the 14-16 mph range but about 800 calories/hour when cycling at 16-18 mph.

Based on my numbers, I would think that 1,000 calories/hour is an overestimation of your calories burned cycling at 12 mph.