There are many factors to consider when determining how many calories you will burn while working out on a rowing machine. If you row at a consistent speed and at a resistance level that you find challenging, you could burn up to 600 calories in an hour. Many people don't work use a rowing machine for an entire hour, however.
The exact number of calories will vary based on the person, machine, resistance, and even the temperature in the room. The best way to estimate the number of calories you've burned is to monitor your progress with your rower's LCD display.