F-Stop & Aperture Calculator
Find the aperture diameter for a focal length and f-number, and the light difference in stops between two f-numbers, free online.
About this calculator
The f-number N = focal length ÷ aperture diameter, so diameter = f ÷ N. Each full stop (f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16) halves the light because the area changes by a factor of 2. Stops between f-numbers = 2·log₂(N₂ ÷ N₁).