In this video

Measure the total vertical distance from the *finished* lower floor to the *finished* upper floor. If the subfloor is exposed on the upper level, place a sample piece of your finished flooring on top of the subfloor before taking the measurement. Similarly, if the lower floor is not finished (e.g., dirt), place a sample of the intended finished flooring (e.g., patio blocks) before measuring. For this project, the finished concrete floor on the bottom and a finished pine floor on top result in a total rise of 36.5 inches (927 millimeters). Additionally, check if the floor is level further away from the stairwell header by extending a level beyond the header and measuring down; use the measurement from where the stringer will actually sit if there's a difference.