According to the Guinness book of World Records, the shortest adult human ever recorded was 57cm (1 foot 10.4 inches) tall, and the tallest was 272cm (8 feet 11.1 inches) tall. But these are extremes. 95% of human heights fall within a range of about one foot.
This is roughly what it would look like if a 272cm tall man stood next to a 57cm tall man. Similarly with the largest and smallest recorded dogs:
I wonder what life would be like for a population of people whose sizes varied much more widely, for example if individuals as tall as 100m and as short as 10cm were not uncommon (but in which the total volume of the people whose size lies in some interval would be roughly proportional to the size of the interval, so there would be a lot more small people than large people). I imagine that such a population would have incredible architecture, as their buildings would have be extremely large (for the tallest people) yet extremely detailed (to be useful for the smallest people).