Submerge the object in a known volume of liquid within a container with graduation markings. Carefully turn the object to release and trapped gases from concavities. Measure the new volume of liquid with the object submerged and subtract the original volume. The difference is the volume of the irregularly shaped object.
If the object is buoyant, choose a lower density liquid or hold the object beneath the surface with a rod or rods, noting the length of rod(s) submerged at the time of the second fluid measurement, then subtract the volume of rod submerged from the difference in the two fluid volumes.
If the object in question is water proof, and small enough. You can measure the amount of displaced water when it is placed in a tank full of water, this may not work for a lot of things but it can help when attempting to measure some objects.
Use volume displacement method.
It is used to find the volume of an irregularly shaped object. An object dropped into a volume of water will displace an equal volume of water.
Mr.Tomak is angry now.
Using a graduated beaker, add water sufficent to totally immerse the object. Note the initial volume of the water without the object. Put the irregularly-shaped object in the beaker and note the final volume. The difference between the final and initial readings is the volume of the object. This is only possible if the object is not soluble in water. If it is, use some other fluid in which it is not soluble.
Google "Archimedes' Principle" and see if that gives you a clue...
You can push it under water / under the liquid's surface, and measure the displacement of liquid.
Finding the center of gravity of an irregularly shaped object can be done using the plumb line method.
To determine the density of an object, you need its mass and volume. If the object is oddly shaped, you can determine its volume by measuring the volume of water displaced when thee object is submerged in a container of water.
the water displacement method
A beaker. Simply fill the beaker with a known quantity of liquid. Drop the object into the beaker, and measure the difference in the fluid levels.
Mass divided by Volume = Density. Or use the displacement method for an irregularly shaped object.
Asteroid
you would use the water displacement theory
If the object in question is water proof, and small enough. You can measure the amount of displaced water when it is placed in a tank full of water, this may not work for a lot of things but it can help when attempting to measure some objects.
Tight
Use volume displacement method.