The most efficient nozzle is generally considered to be that for which the discharge coefficient is nearest unity. Forms and dimensions of the nozzles being equal, the greater the discharge coefficient, the less the jet turbulence becomes. The inefficiency of fire streams is directly attributable to the inital turbulence of the jet and this turbulence has its chief origin in the flow condition inside the nozzle. Thus a knowledge of the discharge coefficients is of great importance in fire engineering. With various smooth nozzles, the coefficients were measured experimentally and the results were discussed theoretically.