This table shows the general container capacity guidelines -- how much cbm fits into each container, as well as dimensions and door height: 

It's important to note that the capacity will be determined by the size of the cartons, how they are packed into the container by the supplier, and whether or not the cargo is palletized. The “stretch to” number is only possible with small boxes.

What are the weight limits?

Weight restrictions vary by carrier, mode, and region. For example, a 44,000-lb load may not exceed the 40' container weight limit set by the ocean carrier, but it will exceed the weight limit for a truck in some states. In this case, the shipment would require a tri-axle chassis or, potentially, an overweight permit. 

Shipments being loaded onto the rail will have their own set of weight limits as well.