Diving tool · Weighting
Dive weight calculator: how much lead do I need?
Enter your body weight, suit, tank and the water you’ll dive in to get a starting estimate and range based on published rules. It is a starting point: you find the right amount with an in-water weight check.
Starting estimate
9.5 kg
between 7.5 kg and 10.5 kg
- Suit and body: 7.5 kg
- Tank (end of dive): +2 kg
The estimate is where your in-water weight check starts, not an exact amount.
Weight check: find the right amount in the water
- Empty your BCD completely. With a normal breath the water should be at eye level; when you exhale you should sink.
- At the end of the dive at 5 m, with about 50 bar left and an empty BCD, you should hover without effort.
- If you check with a full tank, being about 2–2.5 kg heavy is normal; you get lighter as the tank empties.
- Adjust in small steps of about 1 kg.
How the calculation works
We use the starting rules published by training agencies and DAN; they assume ocean-salinity water and an aluminium tank. Tank and water differences are calculated from published cylinder figures and seawater density.
| Input | Rule |
|---|---|
| Suit | 3 mm: 5% of body weight · 5–7 mm: 10% · with hood and gloves +1.5–3 kg · drysuit 10% plus an amount for the undergarment · no suit 0.5–2 kg |
| Tank | An aluminium tank floats at the end of the dive: +2 kg. A steel tank needs about 1.5 kg less lead than aluminium (estimate). |
| Water | The rules assume ocean water. The Mediterranean and Aegean are very close to it; the Marmara surface is −0.85%, the Black Sea −1.3%, fresh water −2.8% (of diver, about 20 kg of gear and lead combined). |
| Range | ±10%, at least ±1 kg. It widens where sources disagree (tank, drysuit). |
Why the right weight, not extra weight?
- Extra lead means more air in the BCD, a head-up position, more drag and faster air use.
- With too little lead you cannot hold your safety stop.
- Make sure your buddy knows how to release your weights.
- The percentage rule tends to overestimate for heavy divers and underestimate for light ones. More muscle needs less lead, more body fat needs more; experienced divers usually need less.
Sources
Sources give no numbers for experience or body build, so the calculation does not adjust for them.
- Scuba Diving (PADI Peak Performance Buoyancy): Buoyancy calculator
- DAN: Weight Up!
- PADI: Why proper weighting is important
- SSI: Buoyancy check
- DUI: Weighting for drysuits
- Faber: cylinder weights
- Catalina S80 aluminium tank (DiveIn)
- Beşiktepe et al. (1994): Hydrography of the Sea of Marmara
- Copernicus Marine: Black Sea physics
- Seawater density calculated with the UNESCO EOS-80 equation.