Weight belts or other weight systems help scuba divers maintain neutral buoyancy underwater. Because of humans’ natural buoyancy, most people would float to the surface without added weight. A full tank of air and a buoyant wet suit increase the diver’s need for added weight. The amount of weight you need to achieve neutral buoyancy depends on several different factors. You cannot use a simple formula to calculate exactly how much weight you need, but you can take certain factors into consideration when estimating how much weight will be ideal.
Weigh yourself. Most divers need added weight equal to at least 6 percent to 8 percent of their body weight to dive in freshwater, and added weight equal to at least 8 percent to 10 percent of their body weight to dive in saltwater. Because saltwater is denser than freshwater, you need more weight for saltwater diving. If you weigh 120 pounds, for example, you need at least 7.2 to 9.6 added pounds for freshwater and 9.6 to 12 added pounds for saltwater. These numbers should serve as starting points rather than final, absolute weight amounts. Depending on your body type and equipment, you might need to wear more or less weight.
Wear additional weight to compensate for a full-body wetsuit or any wetsuit thicker than 3 or 4 millimeters. The thicker the wetsuit and the more of your body the wetsuit covers, the more buoyant you are. When you dive in warm water with just a swimsuit or a shortie wetsuit, you need less added weight than you need when you dive in a full-body wetsuit.
Try on several different weight amounts during practice training sessions in a swimming pool. Wear all your scuba gear, including the wetsuit you wear most often. You should be able to get a sense of how much weight you need.
Make notes in your dive log about any buoyancy difficulties you encounter. For example, if you felt yourself dragging or sinking during a dive, note the problem along with the amount of weight you were wearing, and consider using less weight in the future. If you could not descend at all, note the amount of weight you were wearing, and experiment to find the additional amount of weight that will allow you to control your depth.