Every gearmotor was assigned a service factor in the SEW catalog. The service factor is the ratio between gear unit rated power and rated motor power. There are no standards on how to determine service factors. This is why service factors vary from manufacturer to manufacturer and cannot be compared.
R47DRN90L4 / i=23,28 / Ma [Nm] = 225 / fB 1,3
R47 - Mamax [Nm] = 300
Mamax / Ma = fB
300 Nm / 225 Nm = 1,33 (~1,3)
Refer to the catalog for more information: