Scuba Diving Weight Calculator (How Much Lead Do I Need?)
Estimate how much lead weight to start with for scuba diving from your body weight, wetsuit or drysuit, salt or fresh water and aluminum or steel tank — then fine-tune with a buoyancy check.
How it works
Starting weight = suit allowance + water adjustment + cylinder adjustment · suit: skin 1 kg (2 lb); 3 mm 5% of body weight; 5 mm 10%; 7 mm / semidry 10% + 2 kg (4 lb); shell drysuit 10% + 2 kg (light) or + 5 kg (heavy undergarment); neoprene drysuit 10% + 4 kg (8 lb) · fresh water −2.5 kg (−5 lb) · steel cylinder −2 kg (−4 lb) · rounded to 0.5 kg or 1 lb.
Dive training agencies teach a rule-of-thumb starting point: a 5 mm wetsuit needs roughly 10% of body weight in lead, a thin suit about half that, and thick suits and drysuits a few kilograms more because they trap more buoyant gas. Fresh water is about 2.5% less dense than sea water, so divers need around 2–3 kg (4–7 lb) less, and a negatively buoyant steel cylinder replaces some lead. These numbers are only a start: do a buoyancy check at the surface with a near-empty cylinder — floating at eye level while holding a normal breath — and adjust in small steps.
Worked example
An 80 kg diver in a 5 mm wetsuit in the sea with an aluminum cylinder: 10% × 80 = 8.0 kg of lead, with no water or cylinder adjustment, so start with 8.0 kg (17.6 lb). In a freshwater quarry the same diver would start with 5.5 kg, and with a steel cylinder in the sea with 6.0 kg.
Sources: PADI — Why proper weighting is important when scuba diving · Divers Alert Network — Weight up!
Frequently asked questions
How much weight do I need for scuba diving?
A common starting point is about 10% of your body weight with a 5 mm wetsuit in salt water, 5% with a 3 mm suit, and 10% plus 2–5 kg with a 7 mm suit or drysuit. Then fine-tune with a buoyancy check.
How do I do a buoyancy check?
At the surface with a nearly empty cylinder and an empty BCD, hold a normal breath: you should float at eye level and sink slowly when you exhale. Add or remove 0.5–1 kg (1–2 lb) until you do.
Why do I need less weight in fresh water?
Fresh water is about 2.5% less dense than sea water, so it pushes up less on you and your gear. Most divers drop 2–3 kg (4–7 lb) when moving from the ocean to a lake.
Does an aluminum tank make me more buoyant?
Yes. An aluminum 80 becomes about 2 kg (4 lb) positively buoyant as it empties, while most steel cylinders stay negative, so divers with steel tanks usually need about 2 kg less lead.
Is being overweighted dangerous?
Overweighting forces you to add air to your BCD, which increases drag, air consumption and the risk of uncontrolled ascents or descents. Carry only the lead you need for a safety stop with a near-empty cylinder.
Related calculators
These are starting estimates only. Always confirm weighting with a buoyancy check under instructor guidance and dive within your training.