Sunny 16 rule

I recently learned a very basic thumb rule of photography regarding exposure. It is called the Sunny 16 rule. It states that

On a bright sunny day, the correct exposure of any subject outdoors is 1/ISO at f16.

Example: If you are shooting at ISO 100, then the correct exposure would be a shutter speed of 1/100 and aperture of f16.

A fine tunning of the exposure can be done from this point.

The following site gives you the technique to arrive at correc exposure settings during various ambient conditions.

http://www.fredparker.com/ultexp1.htm