Scuba Weight Calculator

Background.

Divers carry lead because nearly everything they wear wants to float. A wetsuit is foam rubber full of tiny gas cells, the buoyancy jacket holds air, and a body with any fat on it is lighter than seawater. Carry too little and you fight to get down, then struggle to hold a safety stop near the surface as the cylinder empties and lightens. Carry too much and you spend the dive pumping air into the jacket to stay off the bottom, finning harder, breathing your gas faster and risking a descent that is hard to stop.

No formula gets the amount right on paper. It depends on the suit's thickness, the cylinder's material, whether the water is fresh or salt, how much air you habitually keep in your lungs, and body composition: fat floats while muscle and bone sink. Two divers of the same weight can need noticeably different amounts of lead.

What arithmetic can do is give a sensible place to start loading the belt. The page multiplies your body weight by a percentage you supply, the rule of thumb your instructor, dive centre or own logbook uses for your usual set-up, then adds or subtracts a fixed number of kilograms for anything different this time: a thicker suit, a buoyant aluminium cylinder, a move from a lake to the sea.

The real answer comes from a buoyancy check in the water, ideally with a nearly empty cylinder and an instructor or buddy alongside. With the jacket empty and a normal breath held, you should float at eye level and begin to sink slowly as you breathe out. Adjust the lead in small steps until that happens.

What is scuba weight calculator?

Starting ballast is the amount of lead, in kilograms, a diver loads before the in-water buoyancy check: body weight multiplied by the percentage you enter, plus a fixed adjustment for suit or equipment. It is a first estimate of the weight needed to cancel the buoyancy of diver, suit and gear so that you can descend with an empty jacket and still stay down at the end of the dive. It is not a measurement, and no single percentage suits every diver, suit or kind of water.

How to use this calculator.

1. 01Enter your body weight in kilograms, as you would weigh in at home without any gear.
2. 02Enter the baseline percentage you were taught for your usual suit and water, or work it out from your logbook: the lead that passed a check, divided by your body weight, times 100. The default of 8% is only a placeholder.
3. 03Use the adjustment for whatever has changed since that baseline: add kilograms for a thicker suit or for moving from fresh to salt water, subtract them for a steel cylinder or a thinner suit. A negative value is allowed, but the result never drops below zero.
4. 04Load the result, then do a buoyancy check at the surface with the jacket empty, adding or removing small weights until you float at eye level on a held breath.

The formula.

Starting ballast B = m × p ÷ 100 + a, where m is body weight in kilograms, p is the baseline percentage and a is the adjustment in kilograms; if a large negative adjustment would push B below zero, the page returns zero. Body weight stands in for body volume, which sets how much water you displace, and the percentage converts it into lead. The adjustment is a flat number of kilograms rather than a percentage because the buoyancy of a suit or cylinder depends on the gear, not on the size of the person inside it. Each percentage point is worth one hundredth of body weight, 0.8 kg for an 80 kg diver, so the percentage usually moves the answer most. Nothing in the formula knows about water density, cylinder type or body fat; those can only enter through the percentage or the adjustment.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Divers Alert Network. Diving safety guidance current 2026. Buoyancy and weighting safety context. Retrieved 2026-08-06.
2. [2]U.S. National Library of Medicine. PubMed record current 2026-08-06. Indexed derivation and validation literature. Retrieved 2026-08-06.
3. [3]World Health Organization. Patient safety resources current 2026. Clinical decision-support safety context. Retrieved 2026-08-06.