It depends almost entirely on cadence and finish time, because steps are simply cadence multiplied by minutes on the course. A runner holding 170 steps per minute for a 4 hour marathon takes 40,800 steps. The same runner finishing in 3 hours takes 30,600. A walker at 110 steps per minute over 6 hours 30 minutes takes 42,900. There is no single correct number, which is why this calculator asks for your own two inputs instead.
Recreational runners commonly land somewhere between 160 and 180 steps per minute, with faster runners generally turning over quicker than slower ones at the same height. Walking cadence is lower, often near 110 to 120 steps per minute. If you own a GPS watch or a phone running app, use your own average cadence from a long run rather than a preset: it is the single input that changes the answer most.
Divide the distance by the number of steps. This calculator does it for you: a 42.195 km marathon in 40,000 steps gives a step length of about 1.05 metres. A common rule of thumb estimates walking step length as roughly 0.41 times your height, but running step length grows with speed, so a measured step length from a real run beats any height formula.
Usually, yes, because a longer leg tends to produce a longer step at the same effort. But cadence varies more between individual runners than height does, and two runners of the same height can differ by 20 steps per minute. Step count follows cadence and time far more closely than it follows height.
Not automatically. Cadence is one part of a stride, and the useful figure is the one that lets you hold your goal pace comfortably. Deliberately raising cadence changes step length as a consequence, so total step count for the same finish time goes up while each step covers less ground. This tool measures what your stride actually produces rather than prescribing a target.