I found the following article on how to calculate how steep a hill you can cycle up, without needing to exert more effort than normal. He uses a minimum cadence of 60 RPM.
https://www.cyclingabout.com/gradient-threshold-steepest-hill/
You need to estimate your output power. I ran some numbers with my G Line, and it looks to be accurate, compared to my actual riding.
Just for fun, I also calculated if my G Line had a Rohloff hub and a 15T sprocket. With the lower gearing, I'd gain another 3% on the gradient.
You can, of course climb steeper hills (I have), but you need to increase your effort.
by mojoehand