A turbine comprises a turbine wheel for rotation within a turbine housing, the turbine housing including at least one volute arranged to deliver a fluid to the turbine wheel via the turbine nozzle. A method for determining a width of a turbine nozzle for the turbine, comprises selecting from a relationship between a turbine stage efficiency and an effective nozzle area, at least one target effective nozzle area. As used here, the effective nozzle area is dependent on both the width of the turbine nozzle and a whirl angle induced by the at least one volute. The method further comprises determining, in dependence on the whirl angle, the width of the turbine nozzle as a width that will achieve the at least one target effective nozzle area.