Buoyancy Calculator

Getting your weighting right starts with tallying up every source of positive buoyancy you're carrying, and this calculator works through each one using real physical relationships. Your body surface area comes from the Du Bois formula (0.007184 × height^0.725 × weight^0.425), which then scales an estimated neoprene buoyancy contribution — each millimeter of wetsuit thickness over a square meter of covered body lifts roughly 0.8 kg at the surface, with fuller wetsuits and drysuits (which get an extra 2 kg for trapped undergarment air) covering more of that surface area than a shorty. Body buoyancy is derived from a body-density estimate that falls as body-fat percentage rises (since fat is less dense than muscle), compared against the water density you select — salt water at 1.025 versus fresh water at 1.000 — so the same body always needs slightly more lead in the ocean than in a lake.

Tank buoyancy is looked up by cylinder type and reflects real known behavior: aluminum tanks swing 1.2–1.8 kg positive once empty, while steel tanks stay 1.0–1.5 kg negative even empty, a distinction that matters because your weighting must account for a nearly-empty tank at the end of the dive, not a full one. A flat 1 kg is added for BCD buoyancy and a 0.5 kg safety-stop reserve. The calculator also estimates net buoyancy at 10 m, assuming neoprene compresses to roughly half its surface buoyancy at that depth — a useful sanity check, but always confirm final weighting with an actual buoyancy check in the water rather than relying on any formula alone.