The 20 feet, with an internal capacity of 28 cubic meters but used to carry weighty goods, 

while the 40 ft. containers are twice the volume of the 20 ft. ones, able to carry up to 68 cubic meters. but both have the same maximum load weight.

Both 20ft and 40ft containers are no more than 27 and 28 tons in China port can load

FCL shipping means renting an entire container for your shipment.  If you have a large enough cargo to occupy a container, or even most of a container, FCL shipping may make the most economical sense.

It’s also quicker than LCL shipping as there is no need to consolidate or deconsolidate your items from others.

Your container will also remain sealed throughout the journey and unless customs officials select it for inspection will be sealed until it arrives at your address or chosen destination.