This formula considers the gear as a cantilever beam with the full load applied to one tooth. If you enter a number other than zero for the RPM it will derate for dynamic effects of tooth impact. If exact number of teeth is not in the drop down menu, use the closest value.
Lewis Formula: W = S*F*Y / P
W = Safe tooth load
S = Safe material strength (1/3 tensile strength)
F = Face width
Y = Lewis Y factor from table based on tooth geometry
P = Pitch
* 14.5 degree pressue angle gears are about 15% weaker than 20 degree gears.