I use Google Maps with the Terrain View to check out bike ride routes.
Zoomed in all the way on Terrain View, each contour line is 40 feet of elevation. If the distance between the contours where the road crosses the contour line is similar to the width of the hand pointer, then it's steep, well over 10%.
For instance, Cunningham Rd in Cincinnati is known to be 15% on the steep part. Here it is on
Terrain View.
Just browsing around Nashville,
Brick Church Pike looks steep, too. I'm guessing 12% at least.
At this zoomed-in scale, Google's elevations are sometimes just an estimate. So the actual grade can vary from what the map shows, either steeper or shallower.
Anyway, you can find areas of hills (or avoid them!) with Terrain View. And it's easy to estimate the elevation gain of a hill, too. The darker contour lines are 200 feet apart.