It's very simple. Just grab any type of measuring tool (preferably one long enough to span the distance of your well) and measure the widest width (left to right) as well as the distance from the house to the outside edge of you well (front to back). Be sure to measure from the outside of your window wells as your cover will need to extend a little beyond the edges. Our recommended overhang for your overs is 1-3" larger than your well itself.