Scuba weight calculator
A curated heuristic model — a starting estimate, not exact physics. Use it as a scuba lead weight calculator in kg, or switch to lbs: every input and result converts automatically. Looking for a dive weight calculator kg divers in NZ, the UK and AU can use, or a scuba weight calculator lbs mode for the US? Toggle units below. Every factor is published in the methodology section so you can audit the math.
Works as both a salt water dive weight calculator and a freshwater dive weight calculator — pick where you'll dive.
Tank buoyancy swing explainer
Why does tank type change your weighting? Because a cylinder's buoyancy changes as you breathe it empty. An AL80 aluminium tank is slightly negative when full but about 2 kg buoyant when empty — so you must carry that extra lead from the start to stay neutral at the safety stop. Steel tanks stay negative even when empty, so steel divers typically carry 2+ kg less lead. You always weight for the end of the dive (near-empty tank), never the beginning.
Full swing table (typical published values — varies by manufacturer)
Values are typical published full/empty buoyancies in kg (negative = the tank sinks). Real cylinders vary by brand and valve — treat these as representative, not spec-sheet exact.
Salt water ↔ fresh water converter
Salt water is denser than fresh water, so you need more lead in the ocean than in a lake, quarry or pool. Divers use the rule of thumb ×1.0256 (saltwater density ≈ 1025.6 kg/m³ vs 1000 kg/m³ fresh) to convert a known weighting between the two.
This is a rule of thumb for the conversion, not a substitute for a fresh in-water check when you change environments.
Weight-check protocol — the eye-level surface check
No calculator replaces water time. This scuba buoyancy calculator protocol is the interactive version of the classic eye-level surface check — run it step by step at the start of every trip, or whenever you change suit, tank or dive site. Tick each step as you complete it.
Weight distribution planner — belt vs integrated vs trim
Where you put lead matters as much as how much. Think of this as a dive weight belt calculator that also plans integrated and trim pockets: keep enough weight ditchable (weight belt or integrated quick-release pockets) that you can establish positive buoyancy in an emergency — and move the rest to trim pockets near your tank for a flat, horizontal position.
Wetsuit buoyancy table
Approximate lift of a new suit at the surface. Two things erode it: depth (neoprene compresses — a 5 mm suit loses roughly half its buoyancy around 20 m) and age (old, compressed neoprene is far less buoyant). That is why you weight for shallow water and the end of the dive — the most buoyant moment.
Ranges are curated from published weighting guides; your suit's actual lift depends on brand, fit and how broken-in it is.
Quick-reference scuba weight chart
Typical starting lead (kg, salt water, AL80, intermediate diver) — a sanity check for the calculator above:
Methodology — the exact model, published
This tool is a weight calculator for scuba diving that shows its work: a curated heuristic, honestly disclosed as a starting estimate. It is not exact physics — no online calculator can model your lung volume, exact body density or BCD lift. The formula:
Total lead (kg) = 0.02 × body weight + suit lift + water adjustment + tank adjustment + body-composition adjustment + experience adjustment + extra gear, rounded to the nearest 0.5 kg (minimum 1 kg).
| Factor | Values used | Why |
|---|---|---|
| Suit lift (kg) | none 0 · rashguard 0.5 · shorty 1 · 3 mm 3 · 5 mm 5.5 · 7 mm 8 · semi-dry 9 · drysuit 11 | New-suit buoyancy; the single biggest weighting driver. |
| Water | salt +1.5 · fresh −1.5 | 3 kg swing matches the published 2–4 kg salt/fresh difference. |
| Tank | AL40 +1 · AL63 +1.5 · AL80 +2 · AL100 +2.5 · steel 10/12 −0.5 · HP100 −0.5 · steel 15 −1 · twinset −1.5 | Offsets the tank's empty buoyancy so you hold the safety stop. |
| Body composition | lean −1 · average 0 · heavy/buoyant +1.5 | Fat is buoyant (~0.9 kg/L) vs muscle (~1.06 kg/L): buoyant bodies need more lead. |
| Experience | beginner +1 · intermediate 0 · advanced −0.5 | New divers get a small comfort margin; experts trim it away. |
How we compare to other calculators
We hand-checked five scenarios against the published formula of a2zcalculators (base = 10% of body weight, then +2.5 kg salt, +5–10% suit, +1.5–2 kg aluminium tank…). Their documented formula consistently outputs 5–8 kg more than real-world weighting bands — because their own FAQ says the 10% rule already assumes salt water with a wetsuit, yet the formula adds salt and suit adjustments on top again (double counting).
| Scenario | a2z formula (documented) | Dive Weight Lab | Published real-world band |
|---|---|---|---|
| 80 kg, 3 mm, salt, AL80, beginner | 17.3 kg | 9 kg | ~8–10 kg typical |
| 70 kg, 5 mm, salt, steel 12 L, intermediate | 16.8 kg | 7 kg | 6–8 kg (BSAC-tested guide) |
| 90 kg, 7 mm, fresh, AL80, advanced | 17.8 kg | 11.5 kg | 8–12 kg (BSAC-tested guide) |
| 65 kg, drysuit, salt, steel 15 L, beginner | 20.3 kg | 14 kg | 10–18 kg (BSAC-tested guide) |
| 165 lb, 3 mm, salt, AL80, beginner | 16.5 kg / 36 lb | 9 kg / 20 lb | ~18–22 lb typical |
Real-world bands from the BSAC-club-tested weighting guide at African Dive Adventures. Overweighting is the common failure mode of naive calculators — it raises air consumption and ascent risk, which is why we calibrated conservatively and tell you to verify in the water.
Sources
- a2zcalculators — Scuba Weight Calculator (10%-rule formula; comparison baseline)
- African Dive Adventures — Scuba Diving Weight Calculator (BSAC-club-tested real-world bands & weight-check protocol)
- ScubaBoard (salt/fresh ×1.0256 conversion rule; aluminium tank swing consensus)