First determine if your window extends above the top of actual window well. If this is the case, you will want to purchase a bubble style window well cover. If your window is completely below ground level or the top of the window well, you will want to get a low profile or flat style window well cover. Measure the same as above omitting the last measurement.
Measure the actual window well from side to side where the well meets the house, this will give you the width. Now measure from the center of that measurement out from the house to the widest part of the well, this will give you the projection. Lastly, to get the height needed, you will need to measure from that same middle point of the well to the top of the window.
42″ (width) x 17″(projection) x 15″ (height)
You will also need to determine the shape of your window well. MacCourt covers come in circular (which is a half round), elongated (which is a stretched “U” shape) and rectangle (which is rectangular with slightly rounded corners).