DIAMOND COVESCUBAFREE TOOLS · DIAMOND COVE SCUBA
Nitrox, breathing rates and gas planning—nine practical calculators for your next class or dive briefing.
THE DIVER’S TOOLBOX
Choose a tool, check the units and calculate. These open-circuit estimates support your training and team plan; they do not generate decompression schedules or certify a dive as safe.
Depth tools assume sea level: freshwater 34 ft / 10.36 m per atmosphere; saltwater 33 ft / 10 m. Altitude requires a suitable planner. Changing units resets that calculator to example values.
DIVE TOOL 01
Find the depth limit set by your analyzed oxygen fraction.
This is an oxygen depth limit, not permission to dive that deep. It does not evaluate narcosis, gas density, exposure time or decompression.
MOD = (oxygen limit ÷ oxygen fraction − 1) × depth per atmosphere. The displayed whole-depth limit is rounded down.
DIVE TOOL 02
Find the maximum oxygen fraction for a chosen depth and oxygen limit.
The whole-percent mix is rounded down. Analyze the actual fill and recalculate its MOD before diving.
Maximum oxygen fraction = oxygen limit ÷ (1 + depth ÷ depth per atmosphere).
DIVE TOOL 03
Compare nitrogen partial pressure on nitrox with air.
EAD is not an oxygen limit or a decompression schedule. Use the actual depth and analyzed gas in your dive computer. A negative mathematical EAD is displayed as surface equivalent.
EAD = (depth + depth per atmosphere) × (1 − oxygen fraction) ÷ 0.79 − depth per atmosphere. Air is approximated as 21% oxygen.
DIVE TOOL 04
Measure surface-normalized gas use from a steady-depth sample.
For manifolded doubles, enter the combined capacity. Metric capacity is internal water volume, not free-gas litres. SAC in pressure/min depends on cylinder size; RMV allows comparisons. A calm sample is not a stressed emergency breathing rate.
SAC = pressure used ÷ minutes ÷ ambient pressure. Imperial RMV = SAC × rated free-gas capacity ÷ rated pressure; metric RMV = SAC × water volume.
DIVE TOOL 05
Estimate pure oxygen and air additions for a retained nitrox mix.
For trained oxygen-service blenders only. Ideal-gas estimate using 21% air and 100% oxygen; temperature and real-gas effects can change the result. Oxygen-compatible, oxygen-clean cylinders and fill equipment are required for partial-pressure blending. Analyze, label and log the settled final gas. This is not a fill procedure.
Oxygen addition = [final pressure × (target fraction − 0.21) − retained pressure × (retained fraction − 0.21)] ÷ 0.79. Air addition = final − retained − oxygen addition. Negative additions are rejected; no venting instructions are generated.
DIVE TOOL 06
Compare classic thirds with half of usable gas above your planned reserve.
Assumes equal outbound and return consumption in one shared gas supply. Turn when the first team member reaches their limit. This does not calculate minimum gas, match different cylinders, account for current, or plan decompression. Enter a reserve established by your team’s emergency ascent calculation.
Classic thirds turn = 2 × starting pressure ÷ 3. Reserve-based turn = (starting pressure + reserve) ÷ 2. Thirds mode uses the higher threshold so the entered reserve remains available after an equal-consumption return. Turn pressure is rounded up (10 psi or 1 bar).
DIVE TOOL 07
Estimate time to reach an entered reserve at a constant depth.
This is gas-limited time at constant depth—not an NDL or total dive runtime. Descent, ascent, decompression, workload changes and emergencies are not modeled. Your reserve must cover your team’s exit plan. Use combined capacity for manifolded doubles.
Usable gas = (start − reserve) × cylinder gas factor. Duration = usable gas ÷ [surface RMV × (1 + depth ÷ depth per atmosphere)]. Imperial factor = rated capacity ÷ rated pressure; metric factor = water volume. Ideal-gas estimate at sea level.
DIVE TOOL 08
Estimate total and usable gas for a single cylinder or manifolded doubles.
For manifolded doubles, enter combined capacity. For independent cylinders, calculate each separately; this tool does not determine whether their gas is accessible after a failure. Ideal-gas estimates omit temperature and compressibility effects. Metric capacity means internal water litres.
Total gas = pressure × cylinder gas factor. Usable gas = (pressure − reserve) × cylinder gas factor. Imperial factor = rated capacity ÷ rated pressure; metric factor = water volume. Volumes are approximately surface-equivalent.
DIVE TOOL 09
Convert the units you see on cylinders, gauges and dive plans.
Volume conversions only change units. They do not convert cylinder water volume into breathing-gas capacity.
1 bar = 14.503773773 psi; 1 ft = 0.3048 m; 1 cu ft = 28.316846592 L; 1 lb = 0.45359237 kg.
PUT THE NUMBERS INTO PRACTICE
Learn nitrox analysis, gas management and blending with Diamond Cove Scuba in Arkadelphia, Arkansas.
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