You encounter units of mass and volume in a variety of everyday science problems. To determine your mass, you can simply get on a scale, which gives you your mass by dividing your weight by the force of the Earth's gravity. Determining your volume, or the amount of three-dimensional space you take up, requires a more complicated method such as a clever trick that involves using your body to displace a measurable, cylindrical quantity of water. Getting an estimate of your total body volume can be helpful if you're aiming to achieve peak fitness, especially if you need to reduce your volume.
Preparation and Submersion
Fill the barrel about two-thirds of the way with warm, clean water. You must be able to fully submerge yourself without any water splashing over the side.
Measure the distance from the top of the barrel to the surface of the water, in centimeters.
Climb carefully into the barrel, nude or wearing minimal attire. Take a deep breath and submerge yourself completely beneath the surface.
Have your assistant measure the new distance from the top of the barrel to the water surface. Your assistant should indicate to you when he or she is done so that you can come up for air as quickly as possible.
Calculating the Volume
Measure the diameter of the barrel and divide by two to get its radius, r, in centimeters.
Subtract the height of the water surface when nothing was in the water from its height when you were submerged and call this h.
Calculate the volume of the cylinder of water you displaced using the formula Pi * r^2 * h. This gives the volume of your body in cubic centimeters, or milliliters. If you prefer to use liters, divide your result by 1,000.