Oxygen Tank Duration Calculator
Estimate how long your oxygen tank will last based on tank capacity, current pressure, and flow rate.
Enter your oxygen tank specifications and flow rate to calculate the remaining duration for medical or scuba diving use.
Oxygen Tank Duration Calculator
Estimate how long your oxygen tank will last based on tank capacity, current pressure, and flow rate.
About the Oxygen Tank Duration Calculator
Knowing how long an oxygen supply will last is critical in medical care, emergency response, and scuba diving. Running out of oxygen unexpectedly can have severe — or fatal — consequences, so healthcare professionals, paramedics, home-care patients, and divers need a reliable way to estimate tank duration before every session.
The calculation rests on two physical facts. First, an oxygen cylinder stores gas under high pressure; the volume of usable gas (at atmospheric pressure) is proportional to the cylinder's internal water volume and its gauge pressure. Second, a regulator or flowmeter delivers gas at a fixed rate, measured in litres per minute for medical use or in surface litres per minute for diving. Dividing the available volume by the flow rate gives the duration in minutes.
This calculator uses the following approach. The rated (full) pressure is the manufacturer's specification for a fully charged cylinder — commonly 2000 PSI for US E-cylinders, 2015 PSI for many compressed-gas cylinders, or 200 bar in metric systems. The current pressure is the gauge reading at the time you check the tank. The fraction Current_Pressure / Rated_Pressure tells you what proportion of the rated gas remains. Multiply that fraction by the total gas capacity in litres to get the available gas volume at atmospheric pressure, then divide by the flow rate.
For a typical medical scenario: an E-cylinder holds 680 litres of oxygen at its rated pressure of 2000 PSI. If the gauge reads 1500 PSI, the available volume is 680 × (1500 / 2000) = 510 litres. At a flow rate of 2 L/min, the duration is 510 / 2 = 255 minutes, or 4 hours 15 minutes. Adding a safety margin of at least 30 minutes is standard clinical practice — never run a patient's oxygen supply to zero.
For scuba divers, the same principle applies, though the units and rated pressures differ (metric tanks are often rated at 200 or 232 bar, and consumption rates increase with depth due to the increased ambient pressure). Always account for your actual consumption rate at depth, not just the surface flow rate.
Common cylinder sizes in the US include: D-cylinder (~340 L), E-cylinder (~680 L), M-cylinder (~3000 L), and H/K-cylinder (~6900 L). In metric countries, cylinders are described by water volume in litres (e.g. 10 L, 40 L) and pressure in bar. This tool accepts any consistent combination of units as long as you use the same pressure unit for both the current and rated pressure fields.
Always follow the guidance of a licensed healthcare provider or dive instructor when managing oxygen supplies. This calculator provides estimates for planning purposes and should be used alongside appropriate safety margins and professional protocols.
Oxygen Tank Duration Examples
Examples showing tank duration for common medical and recreational oxygen scenarios.
| Scenario | Duration | Available Volume |
|---|---|---|
| E-cylinder (680 L), 1500 PSI / 2000 PSI rated, 2 L/min | 255 min (4 h 15 min) | 510 L available |
| E-cylinder (680 L), 2000 PSI / 2000 PSI rated, 4 L/min | 170 min (2 h 50 min) | 680 L available (full) |
| D-cylinder (340 L), 1000 PSI / 2000 PSI rated, 1 L/min | 170 min (2 h 50 min) | 170 L available |
| Large tank (3000 L), 1800 PSI / 2000 PSI rated, 6 L/min | 450 min (7 h 30 min) | 2700 L available |
| Portable tank (180 L), 2000 PSI / 2000 PSI rated, 3 L/min | 60 min (1 h 0 min) | 180 L available (full) |
How to Use the Oxygen Tank Duration Calculator
- Enter the Tank Capacity in litres — this is the total gas volume at the rated (full) pressure, usually printed on the cylinder label.
- Enter the Current Pressure (PSI) shown on your cylinder gauge right now.
- Enter the Rated / Full Pressure (PSI) — the manufacturer's full-charge pressure; often 2000 PSI for US E-cylinders.
- Enter the Flow Rate in L/min set on your regulator or flowmeter.
- Click Calculate to see the available oxygen volume and how long it will last; always add a safety margin of at least 30 minutes before planning refills.
Frequently Asked Questions
What is the formula for oxygen tank duration?
Duration (min) = (Capacity × Current Pressure / Rated Pressure) / Flow Rate. This gives the number of minutes the tank will last. The fraction (Current Pressure / Rated Pressure) represents how full the tank is. Multiply by the total capacity to get available litres, then divide by the flow rate.
What is the rated pressure for a standard medical oxygen cylinder?
In the United States, standard medical cylinders (E-size) are rated at 2015 PSI, though 2000 PSI is commonly used as a round figure. In metric countries, cylinders are typically rated at 200 bar or 232 bar. Always check the label on your specific cylinder.
How much safety margin should I add?
Clinical guidelines generally recommend a minimum safety margin of 30 minutes for home oxygen therapy and longer margins for transport or emergency use. Many facilities change tanks when the gauge reads 500 PSI (about one-quarter full) rather than waiting until it reaches zero.
Does depth affect oxygen duration for scuba diving?
Yes. As you descend, you breathe denser air, so your actual gas consumption increases proportionally with the absolute pressure (depth in metres / 10 + 1 atmospheres). A diver consuming 15 L/min at the surface will consume roughly 30 L/min at 10 metres depth. Always calculate bottom time using your actual consumption at depth.
Can I use bar instead of PSI?
Yes. As long as you enter both the current pressure and the rated pressure in the same unit, the calculation is correct. The calculator computes the ratio Current / Rated, so the unit cancels out. Enter both in PSI, or both in bar — do not mix units.
What does tank capacity in litres mean?
For medical oxygen cylinders, the capacity in litres refers to the amount of gaseous oxygen stored at standard pressure when the tank is fully charged. For example, an E-cylinder contains approximately 680 litres of oxygen at its rated pressure. This is different from the water volume of the cylinder shell, which is about 4.7 litres.