F-number (disambiguation)

F-number or F number may refer to:

• f-number, the ratio of the lens's focal length to the diameter of the entrance pupil
• 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

See also

• F-ratio (disambiguation)
• F scale (disambiguation)