The table below assumes you have a 50mm lens
and displays the aperture sizes for common f-stops.
Notice also that as the f-stop number increases,
the size of the aperture decreases.
Tips and Tricks
Use a small number f-stop (large aperture) for portraits so you get your subject in focus but not the stuff behind him or her.
Use a large number f-stop (small aperture) to maximize the amount of stuff in focus.
Sunny 16 Rule. At f/16 and in bright, midday sunlight, your shutter speed should be the inverse of your ISO setting to get a good exposure.
Photojournalists sometimes say, f/8 and be there. F/8 gives you pretty depth of field and getting the picture is more important than getting the perfect picture for photojournalists,
who often have to react rather than meticulously setting up shots