Scuba weight calculator
A starting amount of lead for your exact kit, sized so you are neutral at your safety stop with a nearly empty cylinder.
Free to use, no account needed. The calculator loads below.
Weight for the end of the dive, not the start
The single most common weighting mistake is checking your buoyancy with a full cylinder. An aluminium 80 gets about two kilos lighter as you breathe it down, so a diver who is perfectly weighted at the start of the dive is two kilos buoyant at the safety stop, exactly when holding a depth matters most.
This calculator sizes your lead for the end of the dive, with the cylinder at a 50 bar reserve. You will feel slightly heavy on the descent. That is the correct feeling, and it is what a controlled safety stop is bought with.
Where the kilos come from
The breakdown is shown line by line rather than as a single number, because the components behave differently underwater. Neoprene is buoyant at the surface and compresses as you descend, so a thick suit is a large surface number that shrinks with depth. A steel backplate is a constant negative that never changes.
Cylinder material matters more than most divers expect. Steel stays negative throughout. Aluminium starts slightly negative and ends positive. Carbon is very positive empty and needs serious lead, which is the case that most often catches divers out.
The in-water check is not optional
Every coefficient in this model is a rounded average, and real divers vary by around two kilos either side. The number here is where to start, not where to finish.
The check itself: in water too deep to stand, fully deflate your BCD and hold a normal breath. You should float at eye level. Exhale fully and you should sink slowly. Do it with a near-empty cylinder if you can, and adjust in half-kilo steps.
Common questions
How much weight do I need for scuba diving?
It depends far more on your exposure suit and cylinder than on your body. A 75 kg diver in a 5 mm full suit with an aluminium 12 litre in salt water typically starts around 7 to 8 kg. Use the calculator for your own kit, then confirm it in the water.
Why do I need more weight in salt water?
Salt water is denser, so it lifts you more. Most divers remove about two to three kilos moving from the sea to a lake or quarry with the same kit.
Should I be weighted for a full tank or an empty one?
An empty one. You need to be able to hold a safety stop at the end of the dive, when your cylinder is at its lightest and most buoyant. Weighting for a full cylinder leaves you floating off your stop.
Is it dangerous to be overweighted?
Yes, and it is more common than being underweighted. Carrying too much lead means more air in your BCD to compensate, which makes your buoyancy far more sensitive to depth changes, wastes gas, ruins your trim and makes a runaway ascent or descent easier.
The rest of it lives in the app
The app remembers your kit configurations, records what you actually carried on each dive alongside how it felt, and learns your real weighting over time instead of making you re-derive it every trip.