Calculating volume is just another way of saying that you're measuring the amount of space inside a three-dimensional object. You can use standardized formulas for calculating the volume of shapes like cubes, cylinders and spheres, as long as you know their basic measurements.
Calculate the volume of a square or rectangular cube using the formula V = l * w * h. Begin by multiplying length * width * height. So if your cube is 5 cm long, 3 cm wide and 2 cm tall, its volume is 5 * 3 * 2 = 30 cubic centimeters.
Calculate the volume of a cylinder using the formula V = r^2 * (pi) * h. Begin by first finding the area of the circle at one end. Square the radius of the circle and multiply the result by pi, or approximately 3.14. Multiply this result by the cylinder's height to get its volume. So if the base of your cylinder has a radius of 3 cm, its area is 3^2 * 3.14, or 28.26 square centimeters. If that same cylinder is 8 cm tall, its volume is 28.26 * 8 = 226.08 cubic centimeters.
Calculate the volume of a sphere using the formula V = r^3 * (pi) * (4/3). Begin by first cubing its radius. Multiply the result by pi, then multiply this result by 4/3 to get the volume of the sphere. So if your sphere has a radius of 10 cm, that radius cubed is 10 * 10 * 10 = 1000 cubic centimeters. 1000 * 3.14 = 3140, and multiplying that by 4/3 yields a volume of 4186.67 cubic centimeters.
Make sure that any measurements you're using to calculate volume are all in the same unit -- for example you cannot multiply 4 cm * 20 mm, but you can convert the millimeters to centimeters and multiply 4 cm * 2 cm.
Volume can be expressed in cubic centimeters, or in milliliters. One milliliter is equal to one cubic centimeter, or one cc, for short.
If your initial measurements are given in inches, multiply them by 2.54 to convert them to centimeters. You can also convert a result in cubic inches to cubic centimeters, although the conversion factor is different: Multiply cubic inches by 16.3871 to get cubic centimeters.