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Calculations, scales and dive reference

Buoyancy scale

SAC calculator

SAC runs

Weight calc

Pressure

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SAC rate — Surface Air Consumption

SAC is your breathing rate normalised to surface pressure — comparable across dives at any depth. SAC varies significantly with body size, fitness, water temperature, thermal stress, task loading and anxiety level. A larger diver, a cold-water diver, or a diver under stress will naturally have a higher SAC. Knowing your own SAC accurately is what matters — it is the foundation of safe gas planning.

Reference SAC rates

⚠ Broad ranges only — not targets. A larger diver, cold-water diver or diver under load will naturally sit higher. Knowing your own number enables accurate gas planning. Comparing SAC between divers without matching body size, config and conditions is meaningless.

Common tank volumes

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SAC run — controlled measurement

A SAC run is a deliberate, controlled measurement at constant depth — far more accurate than SAC calculated from a recreational dive where depth and exertion vary continuously. Technical and serious recreational divers should have at least one SAC run per rig configuration.

How to conduct a SAC run

Worked example

Note: calculated from actual pressure drop and tank volume — no estimated average depth. This is why SAC runs are more precise than calculated SAC from recreational dives.

My SAC run log

Buoyancy weight calculation

The weight you need equals the positive buoyancy of everything you're wearing and carrying. Neutral calculates this from your rig profile, but understanding the components helps you fine-tune.

Typical component buoyancy values

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💡 The AL80 aluminium crossover: a full AL80 is slightly positive (+0.4 kg). As you breathe the gas down it becomes increasingly negative, reaching maximum negative buoyancy (~+0.8 kg positive — wait, it gets more negative) around 35 bar then stabilises. Plan your weighting for the end-of-dive pressure, not the start.

Pressure & depth reference

Depth / pressure conversion

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Unit conversions

Gear

Inventory

Rig Profiles

A rig profile is a named assembly of gear items. The buoyancy engine uses it to calculate your weight recommendation. Switch profiles on the pre-dive screen.