Wiper motors are rated by stall torque. This is usually expressed in Newton meters (Nm).
A 38 Nm motor is recommended for arm and blade combinations of 28” (710 mm) and longer and for multiple arms and blades driven by one motor.
A 30 Nm motor is suitable for arms and blades in the 20” to 28” (500 mm to 710 mm) range.
A 12 Nm motor is appropriate for arms and blades in the 16” to 20” (400 mm to 500 mm) range.
An 8 Nm motor works well for small arm and blade combinations of 16” (400 mm) and under.
Often motors of 20 Nm or less have internal linkage to make the necessary oscillating motion.