Dive Planning Tools

Gas Consumption, MOD & Best Mix Calculators

Work out your surface air consumption and RMV from a real dive, check the maximum operating depth of any nitrox or trimix at PO₂ 1.4 and 1.6, or enter a depth and get the best nitrox and trimix for it. Every result shows the equation behind it.

Your dive

Enter what your gauge and computer showed. Results update as you type.

Starting pressure

psi

Ending pressure

psi

Tank size

cu ft

Rated capacity, e.g. AL80 = 77.4, HP100 = 100

Tank max (rated) pressure

psi

AL80 = 3000, HP steel = 3442

Average depth

Dive time

min

Water

RMV

—cu ft/min

— L/min

SAC rate

—psi/min

at the surface

Gas used

—cu ft

— psi

Pressure at avg depth

—ATA

— cu ft/min at depth

The equations

1 · Tank factor (cu ft per psi)

TF = Tank sizeMax psi

—

2 · Absolute pressure at average depth

ATA = Depth33 + 1

—

3 · Surface air consumption (SAC)

SAC = Start psi − End psiTime × ATA

—

4 · Respiratory minute volume (RMV)

RMV = SAC × TF

—

Your mix

Pick a common mix or enter your own O₂ and helium. Nitrogen fills the rest.

Oxygen (O₂)

Helium (He)

Mix breakdown

O₂ 18% He 45% N₂ 37%

Water

MOD @ PO₂ 1.4 · working

—ft

— m

MOD @ PO₂ 1.6 · deco / max

—ft

— m

EAD at 1.4 MOD

—ft

equivalent air depth

EAD at 1.6 MOD

—ft

equivalent air depth

END at 1.4 MOD

—ft

equivalent narcotic depth

Minimum depth

—ft

PO₂ ≥ 0.16

The equations

1 · Maximum operating depth at PO₂ 1.4

MOD = ( 1.4FO₂ − 1 ) × 33

—

2 · Maximum operating depth at PO₂ 1.6

MOD = ( 1.6FO₂ − 1 ) × 33

—

3 · Equivalent narcotic depth (O₂ counted as narcotic)

END = ( Depth + 33 ) × ( 1 − FHe ) − 33

—

4 · Equivalent air depth (N₂ only, vs. air's 79%)

EAD = ( Depth + 33 ) × FN₂0.79 − 33

—

5 · Minimum depth for hypoxic mixes

Min = ( 0.16FO₂ − 1 ) × 33

—

Helium doesn't change MOD — only the O₂ fraction does. What helium changes is narcosis, shown by the END. EAD compares only the nitrogen in your mix to air — use it for air-based tables and nitrogen loading.

Your dive

Enter the deepest point of the dive. You'll get the richest nitrox and the best trimix that keep you inside your PO₂ and END limits there.

Target depth (MOD)

Max PO₂ at that depth

Target END (trimix)

Count O₂ as narcotic Most tech agencies do. Unticked, only nitrogen counts, so you need less helium.

Water

Target END guidelines

Standard limit: 100 ft. Most technical diving agencies and teams aim for an END of 100 ft (about 4 ATA) to keep minds sharp and reduce nitrogen narcosis.
Divesoft · Silent Diving · ScubaBoard
Conservative range: 80–90 ft. For heavy workloads, complex tasks, or cold water, many divers restrict their target END to 80–90 ft.
ScubaBoard
Absolute maximum: 130 ft. Training standards rarely recommend letting your working END exceed 130 ft, which matches the traditional max limit for breathing air.
Wikipedia · ScubaBoard

Best nitrox

—

PO₂ at depth: —
END: —
EAD: —

Best trimix

—

O₂ / He / N₂: —
PO₂ at depth: —
END: —
EAD: —
Min depth: —

Closest standard mix that fits

least helium that meets both limits

—

The equations

1 · Pressure at target depth

ATA = Depth33 + 1

—

2 · Best O₂ (rounded down so PO₂ never goes over)

FO₂ = Max PO₂ATA

—

3 · Target END as a pressure

P_END = END33 + 1

—

4 · Helium needed (rounded up so END never goes over)

FHe = 1 − P_ENDATA

—

5 · Check the result

END = ( Depth + 33 ) × ( 1 − FHe ) − 33

—

Nitrogen fills whatever is left: FN₂ = 1 − FO₂ − FHe. Always analyze the fill and re-check it on the Gas Mix MOD tab.

These calculators are planning aids. They don't replace your training, your dive computer, or an analyzed fill. Always analyze your gas and label your tanks with the MOD.