Scuba Weight Belt Calculator
Estimate how much weight to wear for scuba diving.
Based on your wetsuit thickness, body composition, tank type, and water salinity.
How Scuba Weight Belt Requirements Are Calculated
Proper weighting is one of the most important skills in scuba diving. Too much weight wastes air fighting to stay up; too little and you can’t descend or control buoyancy at depth.
Buoyancy Calculation:
Net Buoyancy = Water Displaced Weight − Diver System Weight
To be neutrally buoyant: Net Buoyancy = 0
Starting Weight Estimate
Almost every “rule of thumb” you will read starts at 10% of body weight and then tells you to add for the wetsuit. That double-counts, because the 10% figure already assumes a full 7mm suit. Follow it literally in a 3mm shorty and you end up carrying two or three times the lead you need, which is the exact failure the section above warns about.
The percentage belongs to the suit, not to the diver:
| Exposure protection | Lead as % of body weight |
|---|---|
| Skin or rashguard | 2% |
| 3mm wetsuit | 5% |
| 5mm wetsuit | 8% |
| 7mm wetsuit | 10% |
| Drysuit | 12% (varies hugely with the undersuit) |
Then two corrections, and only two:
- Freshwater: subtract about 2.5% of your loaded weight, which for most divers is 2 to 3 kg. Fresh water is less dense, so it holds you up less and you need less lead to sink.
- Steel tank: subtract about 1.5 kg. An aluminium 80 goes positive by roughly 2 kg as it empties, so it is the baseline here and steel is the discount.
Worked Example: 70 kg diver, 5mm wetsuit, saltwater, aluminium AL80:
- 5mm in salt water: 70 × 0.08 = 5.6 kg
- Aluminium tank: baseline, no adjustment
- Starting estimate: 5.6 kg, call it 6 kg on the belt
The same diver in fresh water drops to about 3.4 kg, and in a 7mm suit climbs to 7 kg. Those are starting points for the buoyancy check below, not final answers.
Fine-Tuning Procedure: Perform a buoyancy check at the surface: with a full breath, you should float at eye level. Empty your BCD completely. If you sink, remove 1 kg. Repeat until you float at eye level with lungs full, and gently sink when you exhale.
Safety Note: Never remove your weight belt underwater. Integrated weight systems should have a quick-release on at least one pocket.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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