⚠️ Educational tool — not dive-planning software
This page is for learning and rough estimates only. Always follow your training, your dive tables, and your dive computer — they account for factors a web page cannot. Never plan a real dive from a website.
Starting range — not a prescription
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Every body, suit, and tank floats differently. Do a proper buoyancy check at the surface: float at eye level with an empty BCD and a normal breath, then adjust in small steps. A steel tank typically needs about 2 kg less, an aluminium tank about 1–2 kg more.
How it's calculated
The estimate uses the rule-of-thumb percentages of body weight that instructors commonly teach as a first guess in salt water:
- Swimsuit or dive skin: about 0.5–2 kg total
- 3 mm shorty: about 5% of body weight, minus a little
- 3 mm full wetsuit: about 6%
- 5 mm full wetsuit: about 8%
- 7 mm full wetsuit: about 10%
- Drysuit: about 10% plus roughly 2 kg, with wide variation by undergarments
Fresh water is less dense than salt water, so the tool subtracts about 2.5% of body weight (roughly 2 kg for most divers) for lakes and rivers. Tank material matters too: an aluminium tank becomes positively buoyant as it empties (add 1–2 kg), while a steel tank stays negative (drop about 2 kg).
Treat the result as a starting range, never a prescription. Body composition, BCD, and suit age all shift the number. Do the check you learned in your course: at the surface with an empty BCD and a normal breath, you should float at eye level and sink slowly when you exhale — ideally with a near-empty tank, or add about 2 kg to compensate for the gas you will breathe off.