What’s the Best Way to Check the Buoyancy of your PFD?

Updated: March 8, 2021

The first test of your personal flotation device (PFD) shouldn’t happen during a boating crisis. Being tossed into unfriendly waters in a life jacket that doesn’t fit or isn’t properly secured can be a potentially deadly mistake that is easily avoided.

Being familiar with your life jacket is the first key to your safety on the water. Understanding its capabilities and limitations may save your life. Is it buoyant enough to keep you above water in a real emergency?

What Do PFD Type Classifications Mean?

Type I Life JacketType I (Offshore Life Jackets)

These have the highest flotation rate. They are meant to accommodate survival for an extended time in open, remote, or rough waters. Most Type I PDFs will roll the wearer into a face up position, even if they are unconscious.

Type I PDFs are rated at 22 pounds for adults, 11 pounds for children, and 7 pounds for infants.

Type II Life JacketType II (Near Shore Buoyant Vests)

These are used by adults and children in calm waters where the chance of being rescued quickly is good. They are rated at 15.5 pounds for adults, 11 pounds for children, and 7 pounds for infants. Baby life jackets are a good example of a Type II PFD.

Type III Life JacketType III (Flotation Aids)

These are used in calm waters where there is a good chance of a fast rescue. They are less bulky than other vests and are often used by paddle-sports enthusiasts. Type III aids are given the same flotation ratings as Type II.

Most youth life jackets are Type III as are most life vest for water sports such as kayaking and jet skiing.

Type IV Life JacketType IV (Throwable Devices)

These may be rings, cushions, or other floating buoys that are not meant for primary flotation devices, but are used to supplement rescue. They have a flotation rating between 16.5 and 18 pounds.

Type V Life JacketType V (Special Use Devices)

These PFDs are employed by whitewater rafters, and professionals who work on or near water sources. They may be specifically designed for use with restricted activities, such as exposure to heat or chemicals.

They may have a buoyancy rating from 15 to 22 pounds, depending on the particular style.


Inflatable vests or belts are activated by a CO2 cartridge that inflates the device when a handle is pulled (manual) or when a water soluble activator is dissolved in water (automatic).

These types are rated between 22 and 33 pounds of buoyancy, and should be checked frequently and re-armed with the activating agent. Inflatable PFDs are a favorite of stand-up paddle boarders.

How Do You Know They’ll Float?

A standard equation on how much buoyancy a person requires is not possible. Below is one scenario often used on other sites:

The calculations for flotation devices are based on the premise that the average human body is comprised of approximately 80% water. The buoyancy of water in the body is equal to the surrounding water, and will not sink.

The average body contains approximately 15% fat. Fat is lighter than water so it will float.

  • The weight of a 125 pound person x 80% water content = 100 pounds of water.
  • The weight of that same person x 15% fat content = 18.75 pounds of fat.
  • 125 pounds of weight – 100 pounds of water – 18.75 pounds of fat = 6.25 pounds.

Therefore, the average 125 pound person weighs approximately 10 pounds when suspended in water. A leaner person will have less flotation due to the lower fat content. Many people think that life jackets for obese individuals require extra buoyancy which is completely incorrect. The opposite is actually true.

The calculation presents similar flotation readings up to 300 pounds. This means that a flotation rating of 15.5 pounds is adequate for most adults. Life jacket ratings of 11 pounds provide adequate flotation for kids up to about 100 pounds and a 7 pound rating is fine for infants.

The problem with this is that there are too many variables. First of all, the water composition of a human body can vary greatly. With babies, about 75% of their bodies are made up of water while adult men and women average about 55-60% water. As we get older, that percentage generally goes down.

Secondly, body fat percentage can vary greatly. An average male is 18-25% fat while an average woman is in the 25-31% range. While it is true that obese individuals typically have an easier time staying afloat since fat will float in water, lung capacity is another factor that determines buoyancy. This is why almost any person that fills their lungs with air and hold their breath will float. Conversely, when we exhale the air out of our lungs, we’ll sink when in water.

Finally, the type of water we’re in plays a roll in buoyancy required. Since salt water (ocean) is more dense that freshwater (lake or pool), it’s easier to stay afloat in the ocean or a saltwater pool.

Combined, there are a million scenarios that affect the amount of buoyancy needed to stay afloat where a simply equation wouldn’t work. But generally speaking, the average adult requires only 7-12 pounds of additional buoyancy to stay afloat. 1

This means that literally any USCG approved life jacket will allow you to float (some better than others).

How Do You Put It To The Test?

Even if you have chosen the right PFD type for your particular activity, it won’t save you if you aren’t wearing it, so it’s important to assure a comfortable fit, and to check your PDF annually for damage that could compromise its integrity.

Testing your life jacket for fit and buoyancy is quick and easy to do. An initial fitting should be made prior to purchase. This is a good time to become familiar with buckles or securing straps and to check for adjustability. A buoyancy test should be done prior to use, and annually thereafter.

The first step in PFD testing is to try it on in shallow water. If it’s properly fitted, it shouldn’t “ride up” as you relax into it. If it does, adjustments should be made until the jacket fits correctly.

As you enter deeper water, lean back and relax into the PDF. It should keep your head well out of the water and allow you to breathe naturally. Notice the distance between your mouth and the waterline. This is known as “freeboard”. The more freeboard you have, the easier it is to float.

Being comfortable in the water as well as on the water will make your watersports outings much safer and more pleasant.

6 thoughts on “What’s the Best Way to Check the Buoyancy of your PFD?”

  1. The flotation calculation above is wrong. 125 lbs X 15% fat = 18.75 lbs of fat (not 15 lbs!), so the final number is 6.25 lbs.

    • Doh! Thanks for noticing. I had a typo on the second bullet point (based off a 100 lb person instead of 125 lb). It’s fixed now.

  2. How many hours or days a lifejacket before it loose its effectivity? Wil it sink after how many days?
    Does it have an expiration?

    • Life jackets don’t really expire. Their physical condition is what determines if they work (no tears, broken straps, etc.). Check out our FAQ page for a more detailed answer.

  3. Please check your equation for accuracy, anyone with a body fat percentage of 20% or higher (which is essentially all women as our normal range is higher) will get a negative number. So based on this, we already float.

    In an adult, a total body water of 80% (more like 70-80%) already includes the fat, correct? If you to subtract the fat out of the total body weight separately in your equation, then you should use a body water percentage based on LEAN body weight (which is more like 75% in infants, 60% in adult).

    • You’re absolutely correct and thanks for bringing this up. There in fact is no one-size-fits-all equation without this turning into an essay paper. The fat percentages include everything. Obviously organs and muscles have a high water density but even bones have some water.

      I’ve updated the article for better accuracy based on my recent research.


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