Heavier weights will help. Don't know that there's a "scale" - just get the heaviest ones you can find. The heaviest ones I know of are from
Manic Salamander - though you can get even heavier ones if you want a throttle lock ("cruise control") as part of the deal too from
Throttlemeister.What may work as well, or better, is to fill your handlebar with something. Popular choices are lead shot, fishing weights, molten lead, BB's or a commercial product like
Bar Snake.Some find that replacing the steel handlebar with an aluminum one does the trick.
Some choose to use gloves with a gel palm.
Also popular is to replace the stock grips with gel or foam grips.
Still others opt for some combination of the above, while some will just choose to live with it the way it is.
As for me, I have a Throttlemeister (purchased for the throttle lock - the vibe damping was a bonus) & gel grips.