Weight belts or other weight systems help scuba divers maintain neutral buoyancy underwater. The amount of weight you need to achieve neutral buoyancy depends on several different factors. There isn't 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. A general rule of thumb states that you will need 8 to 10 percent of your body weight for saltwater dives, and 6 to 8 percent of your body weight for fresh water dives. Always refer back to your scuba training manual for specific buoyancy guidelines.