The spreadsheet shown here provides the average number of cells per field required to achieve 5000 minimum cells on a liquid-based cytology preparation given a certain field of view diameter (13 mm or 20mm) and eyepiece (ocular). For individuals using oculars and preparations not shown, the formula is: Number of Cells Required per Field =5000 / (Area of Circle / Area of Ocular). The diameter of an ocular or microscopic field in millimeters is the field number of the eyepiece divided by the magnification of the objective. The area of the field can then be determined by the formula for the area of a circle (πr2).