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

• Class P
• ClassPad
• ClassPad Educational Tablet
• ClassPad tablet
• ClassPass
• Class prejudice
• Class Proceedings Act
• Class properties
• Class property
• Class-Q
• Class. Quantum Grav.
• Class-R
• Class R
• CLASS R-120 BushCaddy
• CLASS R-80 Bush Caddy
• CLASS R-80 BushCaddy
• Class Relations (film)
• Class representative (disambiguation)
• Class Reptilia
• Class Reunion (1928 novel)
• Class Reunion (Werfel novel)
• Class Rock
• Classroom climate
• Classroom Crisis
• Classroom game