How to Calculate How Long an Oxygen Tank Will Last

How to Calculate How Long an Oxygen Tank will Last (2023)

by | May 19, 2022

An oxygen tank is a pressurized metal container that holds oxygen in a gaseous form. They are made of seamless steel and are helpful in protecting, storing, and transporting oxygen for therapeutic use.

However, oxygen tanks are not equipped with a built-in clock that tells the user how much longer the flow of oxygen will last. The duration of flow must be calculated in order to estimate how long an oxygen tank will last.

Oxygen Tank Duration

In order to calculate the duration of an oxygen tank, you must use the following:

  • Cylinder size
  • Cylinder pressure
  • Gas Flow

In general, the larger the cylinder is in size, the more oxygen it will hold, which means it will last longer than smaller-sized cylinders.

Also, the higher the gas flow, the faster the tank will run out of oxygen.

oxygen tank cylinder sizes

Cylinder Size

The size of a cylinder dictates the amount of oxygen that can be stored inside the tank. The sizes are identified by letter designations, including the following:

  • H cylinder
  • G cylinder
  • E cylinder
  • D cylinder
  • B cylinder
  • A cylinder
  • DD cylinder
  • BB cylinder
  • AA cylinder

Tank sizes E through AA are considered to be small cylinders and are most commonly used during patient transport. Tank sizes H and G are large cylinders and are better suited for stationary patients.

Size E cylinders are the most commonly used oxygen tanks, especially in the hospital setting.

Cylinder Pressure

The pressure of an oxygen tank is directly proportional to the volume of gas inside the tank. Therefore, the higher the pressure, the more oxygen there is inside the tank, and vice versa.

Gas Flow

The gas flow refers to the rate at which oxygen is being delivered to the patient. The higher the gas flow, the faster the tank will run out of oxygen.

The duration of an oxygen tank is inversely proportional to the gas flow.

nebulizer mask from oxygen tank

Formula for Estimating Oxygen Tank Duration

Now that we know the three main factors that dictate how long an oxygen tank will last, we can put them into a simple formula in order to calculate the duration.

The formula for calculating the duration of an oxygen tank is as follows:

Duration (minutes) = (Cylinder Pressure x Cylinder Factor) / Flow

Cylinder Factor

The contents of an oxygen cylinder are specified in cubic feet but must be converted into liters. Each tank size has a different cylinder factor, including the following:

  • D cylinder: 0.16
  • E cylinder: 0.28
  • G cylinder: 2.41
  • H cylinder: 3.14

If you know the cylinder factor, size, pressure, and flow, you can easily plug the numbers into the formula to calculate how long the tank will continue to deliver oxygen.


For example, let’s say you have an E cylinder with a pressure of 2200 psi and a flow rate of 2 L/min. The duration of the oxygen tank can be calculated as follows:

Duration (minutes) = (2200 psi x 0.28) / 2 L/min

= 308 minutes

Therefore, this oxygen tank will last for approximately 5 hours and 8 minutes.


What is an Oxygen Tank?

An oxygen tank is a pressurized metal container that holds oxygen in a gaseous form. They are typically made of steel, which helps protect and store oxygen for therapeutic use.

Oxygen tanks come in several different sizes, which dictates how long the flow of oxygen will last.

What is the Difference Between an Oxygen Tank and Oxygen Cylinder?

There is no difference between an oxygen tank and an oxygen cylinder. Both terms mean exactly the same thing. They are pressurized metal containers that store oxygen in a gaseous form.

Is an Oxygen Tank Explosive?

Oxygen tanks are usually not explosive; however, they can explode under extreme conditions. This includes in a fire or under very high pressure.

In general, you do not need to worry about an oxygen tank exploding. Oxygen tanks are safe to use as long as you follow the proper safety precautions recommended by the manufacturer.

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How Long Does an Oxygen Tank Last?

The duration of an oxygen tank depends on the size of the tank, the pressure of the gas, and the flow rate. The larger the tank, the higher the pressure, and the lower the flow rate, the longer the tank will last.

You can use a simple formula to calculate the duration of an oxygen tank. This will give you a good estimate of how long the tank will last.

How are Oxygen Tanks Filled?

Oxygen tanks are typically filled by connecting the tank to an oxygen concentrator. The concentrator pulls in air from the surrounding environment and filters out the nitrogen.

The remaining oxygen is then compressed into the tank under high pressure, which can be delivered for therapeutic purposes.

What Color is an Oxygen Tank?

Medical gas cylinders are categorized and color-coded by the gas they contain. In general, the standard color for oxygen tanks is green. However, it’s always best to read the label on the side of the tank to verify that oxygen is inside.

When is an Oxygen Tank Empty?

You can confirm that an oxygen tank is empty by checking the pressure gauge. If the needle is pointing to zero, it indicates that there is no oxygen left inside the tank. In this case, no oxygen will flow from the tank.

Who Can Benefit from Using an Oxygen Tank?

Those who are in need of supplemental oxygen may benefit from gas delivery from an oxygen tank.

The primary indication for supplemental oxygen is hypoxemia, which is when the blood oxygen level is below normal. This can be due to a variety of conditions, including COPD, pneumonia, and heart failure.

What Size Oxygen Tank is Best for Transport?

Size E oxygen tanks are most commonly used for patient transport in the hospital setting. They are small enough to move around easily, but they also have the capacity to hold oxygen for an extended period of time.

Outside of the hospital setting, oxygen concentrators are often used for transport. These devices do not require tanks or cylinders, and they can be powered by batteries, making them much more portable.

Final Thoughts

In conclusion, calculating the duration of an oxygen tank is a simple process that only requires a few pieces of information. With this knowledge, you can better estimate how long an oxygen tank will last and plan accordingly.

If you want to learn more, we have a comprehensive guide on medical gas therapy that I think you’ll find helpful. Thanks for reading, and, as always, breathe easy, my friend.

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


  • Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
  • King, Derek, et al. “Gas Cylinders.” National Library of Medicine, 18 Sept. 2021,
  • Blakeman, Thomas C., et al. “Accuracy of the Oxygen Cylinder Duration Calculator of the LTV-1000 Portable Ventilator.” National Library of Medicine, Respir Care, Sept. 2009,

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