To use this lens calculator you need two measurements.
First measure the width of your screen (or other projection surface) in metres.
Then determine where your projector is to be positioned and measure the distance from the front of the lens to the screen, again in metres.

This calculation assumes you are using a 35mm slide in landscape orientation, and that the image fills the width of the slide.

The most common lens found on Kodak Carousel projectors is a 75-120mm zoom lens.
Other Kodak lenses are:
100-150mm zoom
100-200mm zoom
87-200mm zoom
200-300mm zoom
85mm fixed focal length
93mm fixed focal length
100mm fixed focal length
150mm fixed focal length
180mm fixed focal length
There is a wide angle 36mm lens designed for short-throw back projection, but this requires projector adaption.