Estimating an 8 foot width side to side, you can use the formula "100 X rise/run" to convert inches to percent. A one inch rise (a one inch pad under the wheels), would equal 1% of rise.
100 X (1" / 96") = 100 X 0.01041 = 1.041%
At least that's what I learned on the internet.
How do you convert .25 inch per foot into degrees or percent slope
And I know, degrees isn't percent, but I thought the formula was pretty slick.
Here are more formulae for slope calculations, for gradient, percentage and degrees.