What is the empty weight of a Cessna 172?

That depends on the model and year of the aircraft, and what equipment is installed. Cessna started building 172s in 1955, and has built more than 60,000 individual models of the airplane. Different engines, different radiOS & navigation equipment, different interiors all effect the weight of an individual airplane.

The AVERAGE empty weight (no fuel in tanks) of a Cessna 172R, built from 1996 to 1998, is 1691 pounds.