How do we get the exact unit of work? Well, work is done whenever a force (F) is exerted over a distance (d).The amount of work done is proportional to the force (F) and the distance (d). So that is how we get the formula W=F*d. What is the SI unit of F? We have Newton (N). For distance (d), we have meter. So the unit combined is Newton*meter? Technically yes, but we give it a special unit called joule (J), and this unit is in memory of James Prescoot Joule, one of the very first scientists who  truly understood the properties of energy. One joule is defined as the amount of work done when 1N of force is exerted over a distance of 1m.

     In United States, as most of us know, we don't use SI units in real life. We use the units in English system. We use pounds as unit of force and feet as unit of distance, so the unit of work we use is foot-pound (ft-lb). 1 ft-lb means the work done in lifting a weight of 1 poound upward against gravity for a distance of 1 feet.