Plan stair lighting: continuous LED strip length and LED count, or the number of per-step lights.
For a continuous look, a single LED strip runs under each tread nosing; total strip length is the step count times the tread width. For discrete step lights, multiply the step count by the lights per step.
Multiply the number of steps by the tread width to get the total run under the nosings. For 14 steps at 36 inches that is 504 inches, or 42 feet.
Usually one or two recessed lights per step, depending on tread width and how even you want the wash. Wider treads benefit from two.
Common strip densities are 18, 30, or 60 LEDs per foot. Higher density gives a smoother line with no visible dots, useful close to the eye on open risers.