# How long does an Oxygen cylinder last?

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**Calculating Oxygen Cylinder Duration**

**Planning Oxygen Usage**

*Determining How Long Your Oxygen Cylinder Will Last*

**Using the Cylinder Duration Formula**

*Estimating Oxygen Supply Time*

**Step 1: Cylinder Pressure**- Locate the cylinder pressure (psi).
- Subtract a residual pressure of 200 psi to account for errors.
**Step 2: Cylinder Constant**- Refer to the cylinder constant values:
**"D" cylinder:**Constant = 0.16**"E" size:**Constant = 0.28**"M" size:**Constant = 1.56**"G" size:**Constant = 2.41**"H" and "K" size:**Constant = 3.14- Choose the constant based on your cylinder size.
**Step 3: Flow Rate**- Determine the flow rate in litres per minute.
- Typically, regulators provide a maximum of 15 litres per minute.
- Specialist applications may have higher flow rates (e.g., scuba diving, 25 litres per minute).
- Adjust the flow rate as needed (e.g., 6 litres per minute for a nasal cannula).
**Step 4: Calculate Duration**- Use the formula: (Tank pressure - Residual pressure) x Cylinder constant / Flow rate
- Calculate the time in minutes that the cylinder will last.

**Example Calculation**

*Estimating Duration for a "D" Cylinder at 15 Litres Per Minute*

**Step 1:**(2000 psi - 200 psi) = 1800 psi**Step 2:**Cylinder Constant for "D" size = 0.16**Step 3:**Flow rate = 15 litres per minute**Step 4:**(1800 psi x 0.16) / 15 litres per minute = 19.2 minutes**Estimated Duration:**Approximately 19 minutes (rounded down)

Use this formula to calculate the duration of your oxygen cylinder based on your specific parameters.