Evaluate hill gradient I mostly commute and have never had trouble climbing a hill sometimes by using my lowest speeds (or close to them).

How do I evaluate even roughly what grave %age I climbed?

What I mean is that I would love to tour someday in a real mountain-y region, and would like to know how to approach climbs like this.

For example, I see profiles with %ages as high as 10%. I know I never rode 10km at 10% but how does 10% look like? how do I know I won't be forced to give up after the first mile or two?

How about 5%? 7%? or the extreme 12.5% I see on some climbs?

I do have a GPS device that gives a reliable path of where I've ridden, but the altitude is not reliable to the profiles of my rides are not either.
There are various web sites that might help.

I use one called http://ridewithgps.com. You need to register on it but you can get quite a lot from a free account.

Does your GPS device output GPX files? If so, I think Ride With GPS can suck them in. If not you might have to put your route into the site manually (but this is easy enough).

But what you do get on your route is a display of the gradient (you hover over different parts of the route to see it). 

For example, I did a quick ride yesterday afternoon, here it is:



I have a pay account with these people but I'm fairly sure you get this page with the free account too.

Any good to you?

Just added another image - didn't realise SE was going to reduce the main one so much. This is just a zoom of the bit with the tooltip. Note also the blue dot in the corner - this is the location on the google map which corresponds to the crosshairs on the elevation plot.