You may need to use a roof deicing cable calculator to determine how much you’ll need. In some of them, you can plug in your roof’s length, valley length, overhang width, roofing type, and region where you live. Once you hit ‘calculate,’ it will show you the recommended cable length, materials list, and even the potential cost.
You can also estimate it for yourself. You’ll need to measure the roof eaves (edge where the gutters are attached) to find the value of the roof length.
As always, if you’re unsure about your determining how much you’ll need or how to install it, you can always contact a roofing professional for guidance.