That's hard work, isn't it?
Bear in mind the bigger calorie burners are the things that use whole-body movement, like running or swimming. This one doesn't use the lower body at all, where your biggest muscles are. So while it feels 'really hard to do', that doesn't mean it's going to be a huge calorie burner.
You could google it. If you want accuracy on something you can't find online, you'll need to buy and wear a Heart Rate Monitor that gives you a calorie burn estimate.
Deb, in New Zealand