Measurement Tools — Underwater Weighing

What It Is

The percent body fat is calculated from equations based on the density of the body. The density of the body is calculated by an equation that involves measuring a person suspended on a trapeze in the air and then weighing the person under water.

Equipment Used

Special weighing scale and submersion pool or tank

How It's Done

  • The person is seated on a special scale, is submerged in a tank of water, then exhales as much air as possible.
  • S/he remains motionless while underwater while the underwater weight is recorded.
  • This procedure is repeated two to five times to get a dependable underwater weight score.
  • Body density and then percentage of body fat are calculated from the reading


  • It was considered the accepted reference method for many years.


  • The equation is based on studies of standard, young Caucasians. Modifications in the equations may be necessary for other ethnicities.
  • Some people feel uncomfortable when they must be fully submerged, leading to incorrect readings.
  • The procedure requires an experienced operator.
  • There is always air left in the lungs. It is difficult to accurately correct for this.
  • It does not take into account the location of the body fat.

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