I am looking to install a set of steps up to our decking. I am yet to accurately calculate the rise. The ground slopes away from the house so I expect it to be 1700 - 1900mm. I imagine, therefore that I will be looking at 10 or 11 step stringers. (Looking to do 1700 steps so will also be installing a centre brace support.) I'm planning on laying a small concrete slab under the stringers/ brace.
My question: Looking at the 10 step stringer kit by wilmaplex (for example), its specs are that it is for a deck height of 1760 and a width (distance from deck) of 2485. How do I measure where to put the slab?