Anyone know how to calculate calories burned during step pl

I won a session with a personal trainer at my gym. She suggested a specific workout that involves a set with weights/machines alternating with 1 minute of step on a 6 inch step. My heart rate definately goes up and I'm sweating at the end of it. How should I calculate calorie burn for this? Should I even count it as cardio? The entire thing takes me about 40 minutes. Thanks.