Measure the width (side-to-side), depth (front-to-back) and the height (top-to-bottom) of an area with right angles, such as a box or room, and multiply the numbers to calculate total volume. For example, a box with a width of 20 centimeters, a depth of 25 centimeters and a height of 10 centimeters would have a total volume of 5,000 cubic centimeters. For example, 20 x 25 x 10 = 5,000.
Convert the measurement to centimeters if you do not have access to a metric ruler by multiplying the measurement in inches by 2.54 (centimeters in an inch). For instance, 5 inches would convert to 12.7 centimeters, because 5 x 2.54 = 12.7.
Calculate the volume of a cylinder by squaring the radius (distance from the edge to the center), multiplying it by 3.142 (pi) and multiplying that number by the cylinder's height (radius[2] x pi x height). As an example, a cylinder with a radius of 25 centimeters and a height of 40 centimeters would have a volume of 942.6 cubic centimeters. For example, 52 x 3.142 x 12 = 942.6.