Good guide to sunny day aperture settings from Wikipedia.
The basic guide to photography exposure is very simple. If you have a bright, sunny day, then use f-stop 16 for your camera lens aperture. The shutter speed should then be set to the equivalent of your
ISO film speed – or the next number over. For example, if you are using an ISO film speed of 100, your shutter speed should be set to 1/125. More than often, your shutter speed number will be higher than the ISO film speed, but it is much easier to remember that film speed equals shutter speed.