Determine the Rise and Run
To determine the rise and run of the steps, measure the distance from the floor of the deck to the ground and divide that number by 7.5. The result will be the number of steps the staircase will need (e.g., deck is 112" from the ground; 112/7.5 = 14.93. Round up to get 15 steps).
To calculate the actual rise height, divide the height in inches by the number of stairs determined in the last step. In our example, 112/15 = 7.46", which means that the risers will be 7.46" high.
To determine the length your staircase will extend into the yard, multiply the number of steps by the depth of steps. The standard depth for stair treads is 10". In our example, 15 steps x 10" = 150".
Determine the desired width of the staircase, assuming that 36” is a standard width. Once you determine the point where the stairs will meet the ground, mark the area where the concrete footer will go.