A mechanical model is developed to describe the rafting of ice sheets of equal thickness. Rafting is one of the important deformation mechanisms in thin ice. The model predicts the force required to initiate rafting. This force is an upper bound for the force in pack ice. The model is also used to calculate the bending stress developed by rafting. The stress increases in proportion to the square root of ice thickness. Thus for a given ice strength there is a maximum thickness of ice which can raft without fracturing. For typical young ice properties the calculated value of 17 cm is in good agreement with field observation.