How to Calculate How Long an Oxygen Tank Duration Illustration

How to Calculate How Long an Oxygen Tank Will Last (2024)

by | Updated: Apr 10, 2024

An oxygen tank is a sturdy, pressurized metal vessel designed to store and transport oxygen in its gaseous state.

Crafted from seamless steel, these tanks play a pivotal role in ensuring the safe containment and delivery of therapeutic oxygen. However, they lack a direct mechanism to inform users of their remaining duration.

As such, users must calculate the flow duration to accurately determine how long the oxygen supply will last.

How Long Does an Oxygen Tank Last?

The duration an oxygen tank lasts depends on its size, the flow rate at which the oxygen is being used, and the pressure at which it is filled. By calculating the tank’s total volume and adjusting for the flow rate, one can estimate the duration of its supply. It’s always recommended to monitor usage and have a backup supply ready.

Person with Oxygen Tank and Mask Vector

Oxygen Tank Duration

To calculate the duration of an oxygen tank, you must use the following variables:

  • Cylinder size
  • Cylinder pressure
  • Gas Flow

Note: The larger the cylinder is in size, the more oxygen it will hold. This generally means that larger tanks last longer than smaller-sized cylinders. Furthermore, the higher the gas flow, the faster the tank will run out of oxygen.

Oxygen Tank Sizes

The size of an oxygen cylinder determines the amount of oxygen that is stored inside the tank.

Oxygen tank sizes are identified by the following letter designations:

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

Oxygen tank sizes E through AA are considered 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.

Oxygen Tank Cylinder Sizes Chart Illustration

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.

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.

Formula for Estimating Oxygen Tank Duration

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

The formula for calculating oxygen tank duration is:

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

Note: 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 2,200 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

Duration: This oxygen tank will last for approximately 5 hours and 8 minutes.

FAQs About Oxygen Tank Duration

What is an Oxygen Tank?

An oxygen tank is a pressurized metal vessel designed to store and transport oxygen, predominantly in its gaseous form.

It’s used in various applications, from medical treatments to industrial processes and scuba diving.

Is an Oxygen Tank Explosive?

While oxygen itself is not explosive, it does support and accelerate combustion. If exposed to open flames or sparks, the contents of an oxygen tank can intensify a fire.

However, the tank itself will not explode unless exposed to extreme conditions. Proper handling, storage, and safety measures should always be adhered to when dealing with oxygen tanks.

Is an Oxygen Tank Explosive Vector

How are Oxygen Tanks Filled?

Oxygen tanks are filled using specialized compressors or through liquid oxygen systems.

The filling process involves purifying and compressing gaseous oxygen from the atmosphere or transferring it from a larger liquid oxygen reservoir.

This oxygen is then pumped into the tank until it reaches the desired pressure. Safety precautions, including ensuring a cool tank and maintaining cleanliness, are critical during the filling process.

What Color is an Oxygen Tank?

The color of an oxygen tank can vary based on the country and its specific regulations.

In the United States, for example, medical oxygen tanks are typically green. However, in other countries, they may be black or have different color codes.

It’s essential to be aware of local color-coding conventions and always read the labeling to ensure the correct identification of the tank’s contents.

When is an Oxygen Tank Empty?

An oxygen tank is considered empty when the pressure gauge reads near zero, indicating that the volume of oxygen inside has been nearly or completely used up.

However, it’s vital never to let the tank reach absolute zero, especially in medical settings, to ensure patient safety and to maintain tank integrity.

Who Can Benefit from Using an Oxygen Tank?

Oxygen tanks benefit a wide range of individuals and professionals.

Medically, they assist patients with respiratory conditions like chronic obstructive pulmonary disease (COPD), asthma, or those recovering from surgery.

Scuba divers use them to breathe underwater, firefighters rely on them in smoke-filled environments, and mountaineers might use them at high altitudes where oxygen is scarce.

Industries also use oxygen tanks in various processes like welding or cutting.

How Many Liters of Oxygen are in a Tank?

The amount of oxygen in liters contained within a tank depends on the tank’s size and the pressure at which the oxygen is stored.

For instance, a commonly used “E” cylinder can hold nearly 680 liters of oxygen when filled to 2,000 psi. However, there are many different sizes of oxygen tanks, each with its own capacity.

To determine the exact amount of oxygen in a specific tank, refer to its labeling or consult with the manufacturer.

How Long Can I Store an Oxygen Tank?

Oxygen tanks can be stored for extended periods, often several years, as long as they are kept in appropriate conditions.

It’s crucial to store them in a cool, dry place, away from direct sunlight and flammable materials. Regularly inspect stored tanks for any signs of corrosion, damage, or wear.

Even in ideal conditions, tanks should be periodically checked for pressure and refilled if necessary, and always ensure they undergo regular inspections as mandated by safety regulations.

How Much Does it Cost to Fill Up an Oxygen Tank?

The cost to fill an oxygen tank varies based on factors such as the tank’s size, the region or country where the refill is being done, and the current market rates for oxygen.

Additionally, the purpose of the oxygen (medical, industrial, recreational) can also influence the price.

As a general reference, filling a standard “E” medical oxygen cylinder might range anywhere from $10 to $50 or more. It’s advisable to check with local suppliers for the most accurate and current pricing in your area.

What Size Oxygen Tank is Best for Transport?

The best size for transporting an oxygen tank depends on the intended use and duration of need.

Portable oxygen tanks, often used for medical purposes or personal use, are lightweight and designed for short-term use. These can range from “E” cylinders, which are backpack-sized, to smaller “A” cylinders or oxygen concentrators.

For longer durations or more significant oxygen needs, larger tanks may be necessary, but considerations about weight, maneuverability, and transportation safety must be factored in.

Note: Always consult with a supplier or medical expert when determining the best size for transport.

Final Thoughts

Estimating the duration of an oxygen tank is not a mere convenience but often a matter of safety and efficiency.

By utilizing the appropriate formulas and being aware of the key variables, users can make informed decisions regarding tank replacement or refill.

Whether you’re a healthcare provider ensuring a patient has a sufficient oxygen supply or a home oxygen user, accurately predicting oxygen tank duration is an essential skill that guarantees both safety and optimal usage.

John Landry, BS, RRT

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.


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