If you are going to build your own pinhole camera, you can use this calculator to determine the optimum pinhole size of your camera. First, you must determine the focal length of your camera. (This is the distance from the pinhole to the film plane of the camera.) Enter the value in MM and then press the red button. The calculator will help you to find the pinhole size and the f/stop of your camera. Press the red button at the bottom right to reset the calculator if you need to make another computaiton.
The calculator is made by Flash. You may need to download a Flash player if your computer doesn't have one.
Drag the cursor on top of the words of the calculator to see the details.