This was a bad topic to start. I was going to write a definitive reply on how gradients are calculated and what exactly 25% means compared to a 1:4. My research so far has led me to various blogs on the subject where you find about a million different opinions on the subject, most of which are wrong. I've seen mention of reciprocals, trigonometry and a rather demeaning comment along the lines of "everyone should remember y=mx + c from school where the gradient is calculated as rise divided run!", followed by a reply along the lines of: "not forgetting that c represents a large concrete step a car has to get up at the start of any hill".

I think we have the Americans to thank for the % system. It sort of seems okay in that 5 metres up over a distance of 100 metres would be a 5% gradient until you think about a 1 metre ascent over a horizontal distance of 1 metre. This would be a 100% gradient which begs the question "what is a 150% gradient then?". By my reckoning this is not more than vertical but merely a 3:2 hill, that is a 3 metre height gain over a 2 metre distance. Please don't start about ratios at this stage, we can deal with that at another time!

Final thought for now would be how to calculate the gradient of a vertical wall. The vertical height gained could be anything depending on the height of the wall and the horizontal distance would be zero. You can't divide by zero so your f//!ed like you would be if you tried to cycle up it!

I think we have the Americans to thank for the % system. It sort of seems okay in that 5 metres up over a distance of 100 metres would be a 5% gradient until you think about a 1 metre ascent over a horizontal distance of 1 metre. This would be a 100% gradient which begs the question "what is a 150% gradient then?". By my reckoning this is not more than vertical but merely a 3:2 hill, that is a 3 metre height gain over a 2 metre distance. Please don't start about ratios at this stage, we can deal with that at another time!

Final thought for now would be how to calculate the gradient of a vertical wall. The vertical height gained could be anything depending on the height of the wall and the horizontal distance would be zero. You can't divide by zero so your f//!ed like you would be if you tried to cycle up it!