There are a few ways to figure this out. But remember, any site tool that you use is a "guesstimate" and you may have better or worse results once you actually try the antenna at your location. Many, many things can impact an antenna's reception as you will find if you keep looking through the FAQ's. If you are in a good area for reception it's pretty amazing!
We here at Mohu are here to help! The most accurate way is to allow us to perform a free signal analysis at your location. Just shoot us an email with your address to firstname.lastname@example.org or give us a call at 877-825-5572.