F-number (disambiguation)

The f-number is the ratio of the lens's focal length to the diameter of the entrance pupil.

F-number or F number also may refer to:

• F number (chemistry), is a number that can be calculated for polycyclic aromatic hydrocarbons from their structure
• Fujita scale, a rating of a tornado's intensity by its impact on structures and vegetation
• F number in the cross-breeding of hybrid animals such as the Savannah cat, a number that indicates the number of generations of distance from wild stock