there are five assumptions necessary for Little's Law to work, they are: The average input or Arrival Rate (l) should equal the average Throughput (Departure Rate). All work that is started will eventually be completed and exit the system. The amount of WIP should be roughly the same at the beginning and at the end of the time interval chosen for the calculation. The average age of the WIP is neither increasing nor decreasing. Cycle Time, WIP, and Throughput must all be measured using consistent units.