Angle of view of a lens

To use the calculator, either click the 35mm format button, or enter the width and height of the image yourself. Enter the focal length, then click Calculate.

There are no checks on anything as yet. As always, normal people will use millimetres for everything, but it doesn't matter what units you use as long as they're all the same. ("NaN" is Javascript for "Not-a-number", and means someone has done something silly.)