help in calculating grade
Not neccessarily a 50+ topic, but I could use some help.
Trying to calculate the grade of a hill I go up. According to Gmaps pedometer, the hill is .7809 mile, and elevation is 731 feet. Converted the miles to feet and came up with 4123 feet, and calculated a 17% grade. Could this be right? I knew it was a steep hill, but, egad.... 
I think that the basic mistake you're making is that the bottom of the hill is probably not at sea level (0 ft.). You have to subtract the elevation at the bottom of the hill from the elevation at the top (call this value the "rise").
There's also a slight inaccuracy that you'll get by using the distance along the road from the bottom to the top (.7809 miles) as the value to divide the rise by. Strictly speaking, the grade is "rise over run" where the "run" is the horizontal distance from the bottom to the top. If you remember the terminology of a rightangle triangle, the rise is the length of the vertical part of the triangle, the run is the horizontal bottom leg, and the distance you actually ride along to get up to the top is the hypotenuse. For a typical grade of a few percent, however, the hypotenuse is not much longer than the "run", so it's OK to use that as an approximation. 
Typically, anything between 90 and 100 is an A grade, between 80 and 89 is a B grade...........................................:D
Oh, the hill. Looks like your calculations are just about right.......Compared to the exact calculations of the previous post, the difference will be tenths of a percent. 
Here's how I determine the grade of a hill, from the gentlest to the steepest:
breathing easy, can still accelerate breathing harder, would rather not talk, can accelerate with difficulty can feel my heart beating, feeling my legs, can only accelerate by standing muscle burn is setting in should probably stand if I'm going to make it drop into my small chainring on a triple and finally: holy [email protected], please, please, please, make the pain stop. 
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I look on the garmin when I get home or for the road signs. Both of them are wrong for them at this time of the year as this must be a 25%. Seems to flatten out after a couple of months of training though
Garmin shows it as 18% although the camera doesn't but it is only 200yards long. 
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Is a 5% grade considered somewhat difficult, or am I just a weenie? 
Being a weenie is relative. I know 5% for a mile would be very hard for me. (You are probably in the top tier% of your age bracket.) It seems a hill like this that is not too steep would be a good training hill to gain strength.

IMHO, 5% is a significant grade  but then, I am a definite weenie!

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The other thing that makes hill grade percentage calculations all wrong is that a hill may be .5 mile long at a calculated 6% but if say it has a 10 or 12%
section within that number it is a lot tougher climb. I always wondered why I had so much trouble with a short hill in our area until I discovered the middle part of it is 14%! even though the whole thing is less than 10% when you do the math. The road would be illegal to build today according to our township manager. 
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Couple of pics attached and it is nothing. One from the top looking back and it starts from the white cliffs in the background and the other taken about halfway up. 
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