"The required total count of mitoses is per 5 mm² on the glass slide section. With the use of older model microscopes, 50 HPF is equivalent to 5 mm². Most modern microscopes with wider 40x lenses/fields require only 20 HPF to embrace 5 mm2. If necessary please measure field of view to accurately determine actual number of fields required to be counted on individual microscopes to count 5 mm².
(ref: CAP GIST Protocol)"

Field Diameter (mm)#Fields = 3.0 mm2#Fields = 5.0 mm2
0.34271
0.353152
0.37 (my 60x)2847
0.42440
0.451931
0.51525
0.55 (my 40x)1321
0.61118
0.65915
0.7813
0.75711

Calculated by: #fields = 5.0/[(3.1416)*(diameter/2)*(diameter/2)]