Calculating the volume of shapes is usually quite simple, especially when you use simple formulas for regular shapes like triangles, rectangles or circles. However, not all shapes can be classified under these formulas for calculating volume, and sometimes you will encounter these irregular shapes. To calculate the volume of an irregular shape, specifically a shape that can be immersed in water, you must calculate the displacement to find out the volume of your object.
Things You'll Need
 Graduated cylinder
 Water
 String
 Irregular object
 Pencil

Fill a graduated cylinder with water to a certain level and make note of the level of the water. Generally speaking, fill the cylinder so that it is half or just under halfway filled with water. If you complete the experiment and the cylinder overflows, try again with a less water to accommodate for the size of the object.

Tie the string around the object and lower it into the cylinder until it is completely submersed.

Calculate the water displacement to determine the volume of the object. To do this, subtract the water level after the object was dropped in from the initial water level. So, if you lower an object into water that was resting at 10mL and it raises to 30 mL, the water was displaced by a total of 20 mL.

Convert the resulting displacement into a more appropriate unit of measurement; this is the volume of your object. To convert this number, you will have to know what unit is represented by 1 mL of water. The simplest conversion is to change milliliters into cubic centimenters; 1 mL is equal to 1 cm³. Therefore, if the water was displaced by 20 mL, the volume of the object is 20 cm³.
References
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