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Scuba Diving Formulas

Everyday scuba calculations.

Beta: working, still being checked · Alpha: being built · Grey: planned

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Altitude

Altitude Diving Adjustment

Adjusting depths for a dive above sea level.

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ATA

Depth and Pressure

The absolute and gauge pressure at a depth.

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CNS

CNS Oxygen Toxicity

How much of your single-dive and daily oxygen limit a dive uses, as a %.

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Cylinder Contents

Gas in a Cylinder

How much gas a cylinder holds at a given pressure.

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EAD

Equivalent Air Depth

How deep a mix's nitrogen is on air, for narcosis and tables.

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END

Equivalent Narcotic Depth

How narcotic a trimix is, as the depth of air that would feel the same.

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FO₂ / FHe

Best Mix for Depth

The richest nitrox, or the best trimix, for a planned depth.

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Gas Blending

Have / Want / Need

From what is in the cylinder now to the mix you want: top-up and partial-pressure fills.

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Gas Planning (Dive)

Gas Planning - Gas Needed For A Dive

From your RMV, the gas a one-depth dive needs, with its ascent and safety stop.

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Gas Planning (Rock)

Gas Planning - Rock Bottom

The gas to bring you and your buddy up from depth if something goes wrong.

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Gas Planning (Thirds)

Gas Planning - Rule of Thirds

A third of your gas out, a third back, a third in reserve: your turn pressure.

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Gas Weight

The Weight of Your Gas

How much lighter you get as you breathe your cylinder down, and the lead to allow for it.

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MOD

Maximum Operating Depth

The deepest a mix can be breathed before its oxygen passes your limit.

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OTU

Oxygen Tolerance Units

Whole-body (pulmonary) oxygen exposure, for a dive or a run of diving days.

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pO₂ / pHe

Partial Pressure at Depth

The partial pressure of each gas in a mix at a given depth.

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RMV

Respiratory Minute Volume

Your breathing rate at the surface, as a volume of gas per minute.

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SAC

Surface Air Consumption

Your breathing rate at the surface, as cylinder pressure per minute, from a real dive.

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Weighting

Salt and Fresh Water

Your lead in salt water, and what it will be in fresh (and the other way round).

These are formula calculations: they do arithmetic you have chosen to do, with inputs you have supplied. They are not a decompression planner, they do not replace training, and they say so plainly wherever a result could be mistaken for a plan.