How do you measure the volume of a rubber duck?

A body at rest in a fluid is acted upon by a force pushing upward called the buoyant force, which is equal to the weight of the fluid that the body displaces. If the body is completely submerged, the volume of fluid displaced is equal to the volume of the body. That is how we find the Volume of the Irregularly shaped objects.

Archemedes the GREAT GREEK PHYSICIST was in a real problem finding out the formula of how to find the volume of irregular object. After countless failures in finding it, once he was going to get a apparently "BUBBLE BATH", So when he got into the tub the water displaced and got out from the tub resulting in the splash of water. His MIND CLICKED that we could find the volume by submerging the irregular object into the measured water and then substract the displaced water from it. He ran NAKED out of the house because of the happiness saying EUREKA! EUREKA! which literally means "I have found it". Thus this law of Archemedes is also called EUREKA LAW. So to simply remember how to find volume of irregular object keep EUREKA in mind.

if you're asking what comes out, it's steam.