D Cylinder (Factor: 0.16)
E Cylinder (Factor: 0.28)
M Cylinder (Factor: 1.56)
H Cylinder (Factor: 3.14)
G Cylinder (Factor: 2.41)
Custom Factor
Standard safety margin is usually 200 PSI.
Time Remaining
— minutes
(– hours)
How to Calculate Oxygen Flow Rate Duration
In medical settings, calculating the duration of an oxygen tank based on the prescribed flow rate is a critical skill for nurses, respiratory therapists, and EMTs. Knowing precisely how long an oxygen cylinder will last ensures patient safety during transport or in situations where wall oxygen is unavailable.
The Oxygen Duration Formula
To calculate the remaining time (in minutes) of an oxygen cylinder, you use the following standard formula:
Current Pressure: The pressure read from the regulator gauge in PSI (pounds per square inch).
Residual Pressure: The safety margin. It is standard practice not to drain a tank completely to prevent moisture from entering the cylinder. A "Safe Residual Pressure" is typically 200 PSI.
Cylinder Factor: A constant value determined by the physical size and volume of the oxygen tank.
Flow Rate: The amount of oxygen being delivered to the patient in Liters per Minute (L/min).
Common Cylinder Factors
Different tank sizes have different conversion factors. Below is a reference table for the most common medical oxygen cylinders:
Cylinder Type
Factor (L/psi)
Common Usage
D Cylinder
0.16
Portable / Ambulatory
E Cylinder
0.28
Transport / Emergency Carts
M Cylinder
1.56
Home Care / Large Stationary
H Cylinder
3.14
Large Hospital Backup
Example Calculation
Let's assume you have an E Cylinder (Factor 0.28) showing a pressure of 1200 PSI. The doctor has prescribed a flow rate of 4 L/min. You want to leave a safety residual of 200 PSI.
Multiply by Factor: 1000 × 0.28 = 280 Liters of oxygen available.
Divide by Flow Rate: 280 / 4 = 70 minutes.
The tank will last for approximately 1 hour and 10 minutes.
Flow Rate vs. FiO2
While the calculation above determines duration, "calculating flow rate" is sometimes confused with estimating the Fraction of Inspired Oxygen (FiO2). For a standard nasal cannula, the approximation is:
FiO2 ≈ 20% + (4 × Flow Rate in L/min)
For example, a flow rate of 2 L/min would provide approximately 28% FiO2.
Safety Note: Always calculate with a safety margin (residual pressure). Do not wait for the tank to reach 0 PSI before changing it. This calculator is for educational and reference purposes only and should not replace clinical judgment or official hospital protocols.
function updateFactor() {
var selector = document.getElementById("cylinderType");
var customInput = document.getElementById("customFactorGroup");
if (selector.value === "custom") {
customInput.style.display = "block";
} else {
customInput.style.display = "none";
}
}
function calculateOxygenDuration() {
// Get Input Values
var cylinderSelect = document.getElementById("cylinderType");
var cylinderFactor = parseFloat(cylinderSelect.value);
// Handle custom factor logic
if (cylinderSelect.value === "custom") {
var customVal = parseFloat(document.getElementById("customFactor").value);
if (!isNaN(customVal)) {
cylinderFactor = customVal;
} else {
alert("Please enter a valid custom cylinder factor.");
return;
}
}
var currentPressure = parseFloat(document.getElementById("currentPressure").value);
var residualPressure = parseFloat(document.getElementById("residualPressure").value);
var flowRate = parseFloat(document.getElementById("flowRate").value);
// Validation
if (isNaN(currentPressure) || isNaN(residualPressure) || isNaN(flowRate)) {
alert("Please enter valid numbers for Pressure and Flow Rate.");
return;
}
if (flowRate <= 0) {
alert("Flow rate must be greater than zero.");
return;
}
if (currentPressure 0) {
document.getElementById("hoursResult").innerHTML = "(" + hours + " hours and " + remainingMinutes + " minutes)";
} else {
document.getElementById("hoursResult").innerHTML = "(Less than 1 hour)";
}
}