A 150-pound person standing motionless for eight hours burns around 700 calories. In comparison, the same person sitting motionless for eight hours burns 544 calories. It is possible that standing burns more calories because people tend to move around while standing.
Simply standing all day versus sitting all day during a typical 40-hour work week might burn off around 780 extra calories per week. That amount might lead to a loss of 1 or 2 pounds over the course of a year.
Studies of people who sit most of the day find that they tend to die younger than more active people. Standing instead of sitting prolongs life.