Hello,Ms.Hailey
You are right that free checked in baggage for passengers heading from China to U.S. in economy class are two pieces and each weigh less than 23kg. The total length of the three sides of each item should also be less than 158cm.
Generally speaking, hand luggage should be less than 7kg. Those who fly from China to America can only bear one item. The only one handy item should be within 204055 cm and the total length of the three sides should be less than 115cm.
That is the general regulation. Some air company may has special rules. You should also pay attention to the tips on the air ticket or inquire the air company directly.