Oxygen Tank Duration Calculator
Calculate remaining time based on flow rate and cylinder pressure.
D Cylinder (Factor: 0.16)
E Cylinder (Factor: 0.28)
M Cylinder (Factor: 1.56)
G Cylinder (Factor: 2.41)
H/K Cylinder (Factor: 3.14)
Estimated Time Remaining
0 min
(0 hours and 0 minutes)
Est. FiO2 (Nasal Cannula): —%
How to Calculate Oxygen Flow Rate and Duration
For healthcare professionals, respiratory therapists, and patients using supplemental oxygen, knowing how long an oxygen cylinder will last is a critical safety calculation. This ensures that a patient does not run out of oxygen during transport or while waiting for a refill.
The Golden Formula:
Duration (minutes) = [ (Current Pressure – Safe Residual) × Cylinder Factor ] ÷ Flow Rate
Duration (minutes) = [ (Current Pressure – Safe Residual) × Cylinder Factor ] ÷ Flow Rate
Understanding the Variables
To accurately calculate the oxygen duration, you must understand the four key components of the equation:
- Current Pressure (PSI): This is the reading on the regulator gauge attached to the oxygen tank. A full tank typically reads around 2000 to 2200 PSI.
- Safe Residual Pressure: It is unsafe to drain a tank completely to 0 PSI. Standard practice is to subtract a "safety buffer" or residual pressure, typically 200 PSI, to ensure flow does not cut off unexpectedly.
- Cylinder Factor: Different tank sizes hold different volumes of compressed gas. The "factor" converts the PSI into liters of available gas.
- D Cylinder: 0.16 (Common for portable/backpack use)
- E Cylinder: 0.28 (Standard portable tank with wheels)
- M Cylinder: 1.56
- H/K Cylinder: 3.14 (Large stationary tanks)
- Flow Rate (L/min): The prescribed amount of oxygen delivered to the patient in Liters Per Minute, set via the flowmeter.
Example Calculation
Let's look at a real-world scenario to demonstrate the math:
A patient is being transported using an E Cylinder. The pressure gauge reads 1200 PSI. The patient requires 4 Liters/min. We want to leave a safety residual of 200 PSI.
- Determine Available PSI: 1200 PSI (Current) – 200 PSI (Residual) = 1000 Available PSI.
- Identify Factor: E Cylinder factor is 0.28.
- Calculate Volume: 1000 PSI × 0.28 = 280 Liters of Oxygen available.
- Divide by Flow Rate: 280 Liters ÷ 4 L/min = 70 Minutes.
Result: The tank will last for 1 hour and 10 minutes.
Estimating FiO2 from Flow Rate
While the calculator above determines duration, clinicians often need to estimate the Fraction of Inspired Oxygen (FiO2) delivered via a nasal cannula. Room air is approximately 21% oxygen.
A general rule of thumb for standard nasal cannulas is:
FiO2 ≈ 20% + (4 × Flow Rate in L/min)
Example: At 2 L/min, FiO2 is roughly 20 + (4×2) = 28%.
Note: This estimation becomes less accurate at higher flow rates (above 6 L/min) or with mouth breathing, where a venturi mask or non-rebreather might be more appropriate.