1. To calculate field of view, you find the magnification and field number of the microscopes lens in use.
Diameter of microscopes field of view = field number divided by magnification number.
If your microscope uses both an eyepiece and objective lens, multiply the eyepiece magnification by the objective magnification to find total magnification before dividing the field number.
2. Size of an organisms is given by dividing the number of cells in the view with the diameter of the field of view