To estimate the height of the person. You must measure toe-to-toe or heel-to-heel of the same foot (what we'd normally think of as 2 steps) the right and left legs might have different measurements--lots of people have different length legs or slight scoliosis & it will affect their steps.
Women and men have slightly different stride/height relationships, and age matters a lot (think toddlers vs. adults) as does fitness level (grandma vs. marathon running teen). Flat footed people walk differently from high-arched folks, too.
...../|\__ So, if you have a set of prints going any distance, you have to measure
....|.| each gap and then take an average and you have to know whether the
...../ \ person was walking or running.
The quick estimate is:
for Females walking stride length = Height x 0.413
for Males walking stride length = Height x 0.415