H number

H number or H-number may refer to:


 * H-number (photography), an aperture setting used on Rodenstock Tiefenbildner Imagon lenses
 * H number (musical catalogue), a number associated with musical catalogues by Harry Halbreich
 * h-index, an index that attempts to measure productivity and citation impact of the published body of work of a scientist or scholar
 * Herfindahl index, a measure of size of firms in relation to the industry and an indicator of the amount of competition among them