What is the average altatude of a jumbo jet?

The term Jumbo Jet has been generally applied to the Boeing 747.

In my experience, they generally cruise at around 35,000ft to 38,000ft across the Atlantic.

Different models, however, have a SERVICE CEILING* of over 40,000ft but that is not the same as a normal cruise altitude. Most commercial jetliners have a service ceiling of about 42,000 feet.

*defined as the highest altitude at which an aircraft can maintain a rate of climb of 100 feet per minute.