Anyone know of a good way to judge the gradient of hills?

I ride right at the edge of the Texas hillcountry, just North of San Antonio (Boerne, specifically) and to get anywhere requires at least some level of lactic acid discomfort. When I was a distance runner, I used to LOVE to hit the hills. I'd just get this stupid focus on my face and grunt and moan and simulate childbirth while I clumsied my way up it. But now on a bike.....they are a bit more intimidating, and I don't know why.

I need to work on that.