Fitbit vs. hrm

I decided to use both of these today while I was exercising to see what the difference was in calculations between the two of them. My hrm had me at an average heart rate of 149 for an hour and 20 minutes, while the fitbit clocked me at 78 minutes, 5.2 miles. I don't know how effective calculating calories by your heart rate would be, but I'm curious to know which of these devices is closer to correct as far as calorie burn. The fitbit does have my stride length inputted, so I'm fairly sure at least the distance is pretty accurate. Any thoughts would be appreciated...I'm a little lacking in the technology department : )