Tipping the movers is customary in the United States. As with any gratuity it is a show of appreciation for a job well done. It is not mandatory. "Gratuity" has its origins in the Latin word for voluntary.
For a local move, how much to tip should reflect the length of time the move took and the degree of difficulty. Were there flights of stairs involved? A piano? A heavy armoire? Did the mover need to hoist a piece of furniture? Did they navigate a tight narrow staircase successfully?
A waiter / waitress will spend maybe fifteen minutes throughout a meal with you and it is customary to tip 18%. (They did not even cook the food. – For a debate about tipping wait staff see the opening scene of the movie “Reservoir Dogs.”) A mover will move all your worldly possessions and spend anywhere from a few hours to three to four days with you. It is an extremely physical job. That being said, the average tip is $5 to $7 per hour per mover. Depending on the level of quality mover you have chosen, this will be between 5 % and 15% of the move cost.
Once the move is complete the driver will have you sign paperwork and collect payment. You may give the gratuity to the driver. The driver will split the tip evenly themselves and the crew.