You can push it under water / under the liquid's surface, and measure the displacement of liquid.
Google "Archimedes' Principle" and see if that gives you a clue...
The volume of an irregularly shaped geometric object is typically determined by the amount of water it displaces when submerged. This method utilizes the principle of fluid displacement to calculate the volume of the object. By measuring the amount of water the object displaces, one can determine its volume.
Finding the center of gravity of an irregularly shaped object can be done using the plumb line method.
Half fill a graduated glass beaker with water and note the level. Place irregularly shaped object into the beaker. Note the new level. The difference between the two levels is the volume of the object. cw: OK, that method works for objects that don't get wet -- like steel. Tissue paper would not be a good candidate. Also, if the object floats, you have to submerge the object.
Measuring irregularly shaped objects by water displacement is a common technique because it provides an accurate volume measurement regardless of the object's shape. By comparing the volume of water displaced before and after placing the object in the water, you can determine the volume of the object without needing to calculate complex mathematical formulas.
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.
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.
You can find the volume of an irregularly shaped object, like a rock, by using the water displacement method. Submerge the object in a known volume of water in a container. Measure the increase in water level, which equals the volume of the rock.
Mass divided by Volume = Density. Or use the displacement method for an irregularly shaped object.
You can measure an irregularly shaped object by using a ruler, tape measure, or string to measure the object's length, width, and height, and then calculate its volume or surface area depending on the shape of the object. Alternatively, you can use a water displacement method by submerging the object in water and measuring the volume of water displaced to determine the object's volume.
Tight