The number of calories burned on a rowing machine can vary greatly depending on several factors, including the intensity of the workout, your body weight, and the duration of the exercise. Here’s a general guideline:

1. Low Intensity: For a lighter, more moderate rowing session, a person weighing around 155 pounds (70 kg) might burn between 210-310 calories in 30 minutes.
2. Moderate Intensity: At a more vigorous pace, the same person might burn between 260-370 calories in 30 minutes.
3. High Intensity: For very intense rowing, the calorie burn can be significantly higher, ranging from 315-460+ calories in 30 minutes.

These figures are approximate and can vary based on individual differences and specific workout details. For the most accurate measurement, using a fitness tracker or a rowing machine with a built-in calorie calculator is recommended.