The length of time that it takes a Cargo Ship to get from China to the USA is between 15 to 30 days.
The faster a Cargo Ship can go the faster it will reach the USA.
If the cargo ship is empty it can travel faster but when the Cargo Ship is full and carrying cargo then that added weight means the Cargo Ship has to go slower.
Cargo Ships rarely if ever travel and go from one location to another without anything being on them as it costs money to move the cargo ship.
Most cargo ships travel at a speed of between 18 to 24 knots.
The cargo ships usually travel at a speed below capacity to save fuel consumption but at the expense of additional travel time, particularly over long distances.