Body mass index -- or BMI -- is often calculated using only height and weight measurement. The number is the amount of fat on the body and there are defined categories for healthy, underweight, overweight and obese measurements. The accuracy of BMI calculations is often criticized because it does not take into account bone structure, bone density or other factors. According to Harvard University School of Public Health, muscles and bone are heavier than fat. A heavy bone structure could realistically add extra points on your BMI but may not reflect your true body mass.
Hydrostatic Testing
Step 1
Find a location where hydrostatic testing is performed. Some universities offer testing for approximately $30, a of 2011. Speak to your primary care physician about testing facilities in your area. A hydrostatic test may not be covered by your health insurance provider.
Step 2
Sit on the scale that is inside of a tank of water at the testing facility. The assistant will take your measurement out of the water and then measure your weight once your are submerged. You will be asked to blow all of the air out of your lungs.
Step 3
Blow any additional air out of your lungs and hold your breath as you are fully submerged into the tank. The submersion is brief so you will not have to hold your breath for a long period of time. The assistant will record your weight under the water.
Step 4
Find out your BMI. Hydrostatic testing is more accurate then typical BMI calculators because it takes into consideration bone density and bone structure. BMI measurements taken underwater are more accurate because bone sinks to the floor while fat floats. BMI is calculated by measuring the floatation of the body compared to the body weight out of the water.
At-Home BMI Calculation
Step 1
Use a tape measure to measure your height. Record the number on a piece of paper.
Step 2
Step on a scale to find out how much you weight. For a more accurate result, use a digital scale. Record the number on a piece of paper.
Step 3
Calculate your BMI using the following formula. Multiply your weight by 703. Divide the product by your height squared.
Tips and Warnings
- The hydrostatic testing margin of error is 2 to 3 percent and it is dependent on how much air you expel out of the body as you are submerged underwater. A health BMI is in between 18.5 and 24.5. Below 18.5 in underweight and above 24.5 is considered overweight.
- Some individuals experience anxiety due to underwater submersion.
Things You'll Need
- Tape measure
- Scale
- Calculator
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