What This Calculator Does
The Oxygen Tank Duration Calculator estimates how many minutes of oxygen remain in a compressed gas cylinder based on its current gauge pressure, the cylinder's tank conversion factor, and the prescribed flow rate. It is a planning aid commonly used by clinicians, EMS, and respiratory therapists. It is an estimate only and should never replace direct monitoring of the patient and the tank gauge.
How to Use It
Read the current pressure from the regulator gauge in psi. Choose the tank conversion factor that matches your cylinder size (a D cylinder is about 0.16 L/psi, an E cylinder about 0.28, a G about 1.56, and an H/K about 3.14). Enter the oxygen flow rate in liters per minute. The calculator returns the estimated remaining duration in minutes and an approximate hours-and-minutes breakdown.
The Formula Explained
$$\text{Duration (min)} = \frac{\text{Gauge Pressure} \times \text{Tank Factor}}{\text{Flow Rate}}$$ The tank factor converts pressure into available volume of usable gas for a given cylinder, so multiplying it by gauge pressure gives the liters remaining. Dividing by the flow rate (L/min) yields the minutes of supply.
Worked Example
An E cylinder (factor 0.28) reads 2000 psi and is set to 2 L/min. $$\text{Duration} = \frac{2000 \times 0.28}{2} = \frac{560}{2} = 280 \text{ minutes}$$ or about 4 hours and 40 minutes.
FAQ
Should I plan to empty the tank? No. Always keep a safe reserve (often a switch at 200–500 psi) and account for transport time.
Where do tank factors come from? They are standard published constants representing usable liters per psi for each cylinder size.
Does flow rate affect accuracy? Higher flow shortens duration proportionally; the result assumes a constant flow.
