Replacing AC motor with servomotor

In an upgrade of a machine we will replace an AC motor with a servomotor.
Because we don't know the mechanical specs of the load on the motor, we can only base on the power of the AC-motor.
We have no torque data available of the AC-motor, only Kw and rpm. If we take a servomotor with approximately the same Kw and nominal rpm, can we suppose then that our servomotor has at least as much torque to drive the load?
I also investigated some AC-motors and servomotors, and saw that for AC-motors and servomotors with same Kw and rpm the inertia is about 3-4 times lower for the servomotors.
What impact could this much lower inertia of the servomotor replacing the AC-motor have?

most servo motor suppliers will do those calculations for you
that is part of their service and sales
the biggest issue with a standard AC motor is stating it, assuming no VFD.
Servo's can be designed to use less power depending on both load and inertia.

If your inertias are mismatched, then your servo motor won't be controllable. You really need to figure out your load inertia. Load to servo motor inertia maximum values vary from model to model. 6:1 is usually safe for most models. Some claim up to 20:1(Yaskawa Sigma-5 is one). Another option is installing a gear head. A 3:1 will bring your inertia down. Servo motors can usually run faster than induction motors, so that might work.

Highland Controls said:

If your inertias are mismatched, then your servo motor won't be controllable. You really need to figure out your load inertia. Load to servo motor inertia maximum values vary from model to model. 6:1 is usually safe for most models. Some claim up to 20:1(Yaskawa Sigma-5 is one). Another option is installing a gear head. A 3:1 will bring your inertia down. Servo motors can usually run faster than induction motors, so that might work.

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If for instance I bring the gearhead reduction from 10:1 to 20:1, will the load inertia then be devided by two?