Calculate the vertical distance from the finished floor landing to the finished floor surface of the upper floor to find the total rise. Divide the distance by the desired height of the riser. Round the result up or down to the nearest whole number if the result is a fraction.
Divide the vertical distance by the rounded up whole number. The result is the required number of risers.
Find the tread width -- stair run -- by using the riser-tread ratio formula: 1 riser plus 1 tread = 17 inches minimum. If the riser is 7 inches, the tread is 10 inches. Make sure any adjustments are less than the maximum 18 inches.
Make adjustments to calculations, not individual risers and treads, to fit within the minimum and maximum dimensions in the tread-riser relationship. Each riser and each tread must be consistent for the finished staircase.