If you are properly weighted in freshwater and you know the total weight of you and your equipment, add 3% of that total weight going to saltwater. The simple fact is that saltwater is 3% denser than freshwater, and so the buoyant force acting on you in saltwater is 3% greater than in fresh (and if you're neutral, that force in fresh is equal to your weight.)
For most people, this means if you and your equipment weigh 130 pounds you should add 4 pounds. If you weight 270 pounds, you should add 8 pounds. If you're in between, add something in between.
Of course this assumes you are properly weighted in FW to begin with and you'll be using the same equipment in both environments.
For most people, this means if you and your equipment weigh 130 pounds you should add 4 pounds. If you weight 270 pounds, you should add 8 pounds. If you're in between, add something in between.
Of course this assumes you are properly weighted in FW to begin with and you'll be using the same equipment in both environments.