VALLEY WIDENING RATE QUESTION: How fast is the valley widening in millimeters/year? at 20.1464 -155.6388 Step 1: If you zoom in, you can see the 30 m pixels (30 m long, and 30 m wide; the diagonal of a pixel is 42.5 meters). The avatar is standing at the mouth of a valley, on one side. Your task is to measure the width of the valley. In almost all cases, the width of the valley is best measured by using the diagonal length. So just count the number of pixels across the valley mouth and multiply by 42.5. That is the valley width in meters