Dive & breathing-gas planning
Know the pressure. Plan the gas.
Check analyzed Nitrox, maximum operating depth (MOD), oxygen partial pressure (PO₂), surface air consumption (SAC) and respiratory minute volume (RMV).
33 ft seawater = 1 ATA
34 ft freshwater = 1 ATA
1 ATA = 14.6959 PSI
01
Converter
Depth & pressure
Depth—feet seawater
Depth—feet freshwater
Gauge pressure—ATA above surface
Absolute pressure—ATA including atmosphere
Absolute pressure—bar
Absolute pressure—PSI
Absolute pressure—mmHg
02
Nitrox
MOD, PO₂ & best mix
Maximum operating depth—fsw
PO₂ at planned depth—ATA
Pressure at planned depth—ATA absolute
Maximum theoretical O₂—at planned depth and limit
Maximum whole-number mix—rounded down; verify analyzed gas
Show Nitrox formulas and cautions
MOD = (selected PO₂ limit ÷ oxygen fraction − 1) × 33 fsw or 34 ffw.
PO₂ at depth = oxygen fraction × absolute pressure in ATA.
Maximum theoretical mix = selected PO₂ limit ÷ ATA at the planned depth.
This calculation does not account for decompression obligation, oxygen exposure, gas density, workload, altitude, equipment limits, agency policy, or individual susceptibility. Analyze and label every cylinder before use.
03
Gas planning
SAC, RMV & duration
Surface SAC—PSI/min
Surface RMV—ft³/min
Target pressure—ATA absolute
Use at target—PSI/min
Gas use at target—ft³/min
Available gas—ft³ above reserve
Show formulas and assumptions
Depth ATA = depth ÷ 33 (seawater) or 34 (freshwater) + 1.
SAC = pressure used ÷ minutes ÷ ATA at test depth.
Cylinder constant = rated volume ÷ rated pressure. RMV = SAC × cylinder constant × cylinders used during the measured segment.
Available gas = target-dive cylinders × (starting pressure − reserve) × cylinder constant. Duration = available gas ÷ (RMV × target ATA).
How the calculations work
Nitrox and dive gas questions
How is Nitrox maximum operating depth calculated?
MOD = (selected PO₂ limit ÷ analyzed oxygen fraction − 1) × 33 feet in seawater, or × 34 feet in freshwater. For 32% oxygen at a 1.40 ATA limit in seawater, the result is about 111 feet. Verify the analyzed mix and use the appropriate limits for the dive.
What is the difference between SAC and RMV?
SAC here is the pressure drop per minute at the surface, normalized from a measured segment at depth. RMV converts that rate to volume using the cylinder’s rated capacity and pressure, including how many cylinders fed the diver during the test.
Does the gas-duration estimate include ascent or team reserve?
No. It estimates usable time at one target depth above the entered reserve. Ascent, decompression, contingencies and shared gas require a separate dive plan under the applicable training and agency rules.
Planning and training aid only
Not a dive plan, decompression table, gas-management protocol, or substitute for agency policy, qualified supervision, equipment checks, current Navy/NOAA tables, and appropriate reserve rules. Always independently verify the inputs and results.
Formulas, examples & assumptions
Content updated October 10, 2026 · Created by Bryan Fleck. Independently verify measurements and scoring assumptions.
Nitrox MOD and oxygen partial pressure
PO₂ (ATA) = analyzed oxygen fraction × ambient absolute pressure. MOD = (selected PO₂ limit ÷ oxygen fraction − 1) × depth per atmosphere. This model uses 33 ft/ATA for seawater or 34 ft/ATA for freshwater.
Example: 32% oxygen at a 1.40 ATA limit gives 111.4 ft in seawater, about 34.0 m. Round and apply limits under your training procedures; analyze the actual gas.
SAC, RMV and estimated duration
Pressure SAC = cylinder pressure used ÷ test minutes ÷ absolute pressure at test depth. RMV = pressure SAC × rated surface volume ÷ rated pressure × cylinders feeding the diver during the test. Duration = usable surface gas ÷ (RMV × target absolute pressure).
Example: 20 L/min surface RMV at 3 ATA uses 60 surface-equivalent L/min. A usable 1,200 L lasts an estimated 20 minutes at that depth.
Reserve and depth assumptions
Duration here is time at one entered depth above the entered reserve. It does not budget ascent, decompression, a gas switch or a second diver. Pressure-based SAC depends on cylinder size; volume-based RMV makes comparisons more useful.
For team ascent gas, use the dedicated emergency-reserve tool and independently verify the applicable dive plan.