Singing won't get you to shed pounds the way running or a gym workout does, but singing standing up will burn a number of calories comparable to walking, yoga or light housework. Even when sitting, singing improves lung and heart function, and more serious training brings more serious aerobic benefits, increasing the rib cage volume and respiratory function.
As with all activities, calories burned singing depend on the weight of the person doing the singing, as well as a body position and associated other activities. A person weighing 150 pounds will burn approximately 100 calories singing for an hour while sitting down, and a 200-pound individual will burn about 140 calories. Stand up to belt out those tunes and the calories burned increase to 140 for somebody weighing 150 pounds and 180 for a 200-pound person. If you move while singing, whether playing an instrument, dancing or acting on stage, extra calories will be burned, depending on the intensity of the movement.
A 2006 study in Folia Phoniatrica and Logopaedica reported that even over a few months of vocal training, the lung volume and rib cage and abdominal expansion -- the latter to do with diaphragm -- increased. The American Journal of Nursing reported in 1986 that opera singers had stronger chest wall muscles, better pumping hearts and maintained their lung capacity until older age.