As others have said, microwave ovens vary so much in power that it is impossible to answer this question. One thing I do, though, to save time and heat (my kitchen is not air conditioned, not an issue right now, at -6 degrees, but in the summer a real issue) is nuke potatoes until they are almost done, then throw them into a very hot oven for maybe five minutes to get that good "skin", or throw them on the grill for the same effect. I had to buy a new microwave oven a couple of years ago and still hate the darned thing. Cannot get my timing right. Has less power than my old one, and no real instructions on baking potatoes! For the most part, you can go to your owner's manual and find the timing for it. By the way, baking a potato until it is almost done, then cutting, grating, slicing it for another preparation (anything from scalloped potatoes to home fries to hash browns) cuts a lot of prep time down, lets you cook with less fat, and keeps the heat down in the kitchen.