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‘What size PFD do I need?’
‘Do lifejackets have a weight limit?’
These are just two questions (of many) that regularly surface when kicking off conversations about getting marine enthusiasts into the best PFD or life jacket for their adventures. into the best possible PFD for their adventures.
Whether you're looking for a PFD for a specific activity or trying to figure out what life jacket best suits your weight, we’ve lined up expert insights from the engineers here at Mustang Survival to help guide your PFD or life jacket selection. From kids' flotation options to adult PFDs—and even a PFD for dogs—we’re here to help you confidently navigate fit, function, and PFD sizing.
The answers to the ‘best PFD or life jacket’ questions might surprise you - and it’s all based on science. Come along for the ride as we explain buoyancy and how choosing a PFD comes down to two simple questions.
What is Buoyancy?
Buoyancy is the upward force of a body of water or fluid that gets applied to any object entering it, that opposes the weight of that object, whether fully or partially submerged. The amount of buoyancy applied to an object is dependent on how much water the object moves (or displaces) when it enters the water.
If the object moves less water than its weight, it’ll sink. If it moves more or an equal amount to its weight, it will float.
What’s interesting is what happens to, and with, the human body while in water. And, how the principles of buoyancy involve thinking beyond weight, and into a whole world of factors. Essentially—and in an oversimplified statement—bodies get lighter. A LOT lighter.
How Much Buoyancy is Required?
The United States Coast Guard has published on their Boating Safety website that ‘most adults only need 7 to 12 pounds of buoyancy (31 to 53 Newton) to keep their heads above water’.
A great example is the MIT 70 Automatic Inflatable PFD, one of our most low-profile and comfortable options for boating. With 15.7 pounds of buoyancy (70 Newtons) and a compact design, it strikes the ideal balance between safety and comfort, making it one of the best PFDs for adults.
How Does Buoyancy Get Calculated?
There is no ‘one equation’ that computes weight into in-water weight; factors like body composition, height, shape, weight distribution, and aspects of the physical body unique to each human being are too vast to reliably and consistently quantify it. Something as simple as someone inhaling can affect their body’s buoyancy (making them more buoyant as they fill their lungs, and less when they empty them).
Nonetheless, there is a general rule-of-thumb system put into place that takes into account all these nuances.
See below for example calculations.
A common misconception is that individuals with a higher body weight assume they need a PFD PFD or life jacket that offers the highest amount of buoyancy (the greatest number of pounds of support). When in actuality, a body’s weight on land doesn’t indicate how much poundage you need. Its composition is what brings buoyancy into perspective: the leaner (the less body fat you have), the higher buoyancy you require. This is where a life jacket fit guide can help you determine what works best for your body type.
The Engineering Behind Mustang Survival PFDs
When Mustang Survival engineers create a new PFD or life jacket or optimize an existing one, they go beyond simply designing something to bring the wearer to the water’s surface. Depending on the PFD sizing and design, they also aim to turn the wearer onto their back while floating.
Their focus is on engineering precise angles: the angle of the wearer’s face to the water and the position of their mouth when floating. The goal is to ensure that the head and mouth are as high out of the water as possible. As a result, the best PFD or life jackets consider more than buoyancy as a means of providing lift or upthrust to raise the wearer above the surface.
Here’s where it gets tricky: body weight and weight distribution *can* impact those angles they engineer for. It’s something that can’t be avoided (again, with the uniqueness of each body), yet should be noted when choosing the PFD best suited to you, and what you’re heading out to do.
Does Everyone Require the Same Buoyancy?
Choosing the right personal flotation device (PFD) or life jacket isn't just about style or fit—it's about understanding how much buoyancy you need to stay afloat, comfortably and safely, in real-world conditions.
Buoyancy is the upward force that keeps you afloat in water. But contrary to popular belief, more isn’t always better—you want just enough lift for your body type, activity, and environment.
Below, we break down common buoyancy questions our Customer Experience team receives to help you make a confident, informed choice.
How Much Buoyancy Do Adults Need in a Life Jacket?
Most adults need between 7–12 lbs (31–53 Newtons) of buoyancy to stay afloat with their head safely above water. The exact number depends on several factors:
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Body composition: Leaner individuals or those with low body fat often need more buoyant lift.
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Size and weight: Larger adults may require more lift, especially if wearing heavy gear.
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Clothing layers: A life jacket needs to counter the added weight of boots, jackets, and gear in the water.
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Environment: Calm inland paddling requires less buoyancy than rough offshore boating or cold-water rescue.
Higher-buoyancy options, like inflatable PFDs, provide 15 lbs or more of lift—great for anglers, offshore boaters, and professionals who want less bulk but need reliable flotation.
Quick Example…
Let’s say you weigh 180 lbs (about 82 kg). You don’t need 180 lbs of buoyancy to stay afloat—your body is already mostly water, which is neutrally buoyant. On average, only 8–12 lbs of lift are needed to keep your head and airway safely above water. That’s where your PFD comes in.
For a more in-depth example that breaks it all down, click here.
Want to learn more about inflatable options? Explore the different types of inflatable PFDs in our guide.
How Much Buoyancy Do Kids Need in a Life Jacket?
Unlike adult PFDs, children’s life jackets aren’t labeled by pounds of buoyancy—they’re sized by body weight ranges. This ensures that each design provides the right lift and flotation angle for a child’s unique proportions, especially their larger head-to-body ratio.
Children’s PFDs are engineered to:
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Keep a child’s head above water
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Support face-up flotation
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Remain snug during play or movement
Why You Can’t Use a Formula for Kids
Buoyancy isn’t one-size-fits-all, especially for kids. Factors like muscle mass, body fat, and posture all influence how a child floats. That’s why we build kid-specific safety features (like grab handles and head support) into each weight category.
Dive deeper: Most Asked Kids’ PFD Question
How Much Buoyancy Does a Dog Life Jacket Need?
There’s no standard “buoyancy number” for dogs, but that doesn’t mean performance should be a guessing game. A good dog life jacket—like our Underdog Life Vest—should be chosen based on:
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The dog’s weight and breed
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Body shape and buoyancy needs
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Swimming ability and activity level
Look for these key features:
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Full-body support and head flotation
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Grab handle for easy lift-in/out of the water
Adjustable straps for a secure, balanced fit
We recommend trying the jacket in shallow water first to make sure your pup floats safely and comfortably, before heading out on longer trips.
Example Calculation
To understand how personal flotation devices (PFDs) keep you afloat, let’s break down the physics using a 200-pound person as an example. Roughly 80% of the human body is water, which effectively weighs nothing in water, leaving only 20% of body weight that must be supported.
That’s 200 lbs × 20% = 40 lbs.
At first glance, this may raise questions since many life jackets offer only 15–22 lbs of buoyancy. But body fat also plays a crucial role: about 15% of body weight is fat, and fat is lighter than water.
So 200 lbs × 15% = 30 lbs of fat providing natural flotation. Subtracting that from the 40 lbs needing support leaves just 10 lbs that the PFD must keep afloat.
For added context, a PFD with 22 lbs of buoyancy provides more than double the lift needed in this scenario. Even someone weighing 250 pounds with a similar fat percentage would only require about 12.5 lbs of assisted buoyancy (250 lbs × 20% = 50 lbs; 250 lbs × 15% fat = 37.5 lbs; 50 – 37.5 = 12.5 lbs).
This makes it clear why Level 70 PFDs with 15.7–22 lbs of buoyancy are sufficient for most adults; they're engineered to keep your head above water, even in unexpected conditions.
Life Jacket Levels: What They Mean
Life jackets are rated by levels based on buoyancy and performance.
Level 70 (USCG/TC) is best for inland waters and active use, offering reliable flotation without face-up rotation. Level 50 is a buoyancy aid, not a life jacket—ideal for strong swimmers in calm conditions.
Choosing the best PFD for you.
With a science-backed understanding of how buoyancy works, and knowing there are many choices you can make when it comes to your PFD selection, here are the top two questions to consider when narrowing down your search:
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What are you doing?
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Where are you going to be?
Pro Tip: When in doubt, go with higher buoyancy, especially in offshore or unpredictable environments. To help make a streamlined choice, buoyancy calculators are available online.
Also, remember, a life jacket that isn’t well-maintained defeats its purpose. For a more in-depth guide to PFD maintenance and inspection, take a look at our resource here.
What Activity are You Doing?
Activity matters as there are PFDs that are best suited for certain kinds of adventures, and some that are certified for sure on or in specific watercraft. And, some PFDs offer incredible amounts of buoyancy, yet are cumbersome, limit mobility, and take up a lot of space on deck. Understanding the demands of your activity can help you choose the best vest for your pursuits.
Here’s what to look for:
Boating
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Look for: high visibility, easy storage, and all-day comfort
It’s important to ensure that each person on the boat has a properly fitted and suitable life jacket for their size and needs.
Mustang Pick: MIT 150 Convertible Inflatable
Features: 38 lbs of buoyancy and offshore-ready
Fishing
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Look for: Pockets, high-back designs, and breathable materials. Women may benefit from fishing PFDs specifically designed for their body shape to ensure comfort and safety.
Mustang Pick: Accel 100 Fishing Vest
Features: Built for anglers, with tons of storage
Paddle Sports (kayaking, SUP, canoeing)
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Look for: Mobility, ventilation, and ergonomic design
Mustang Pick: Khimera Hybrid PFD
Features: Light, flexible, and dual-buoyancy
Where Are You Going to Be?
Offshore in 6-foot high waves, or inshore enjoying the shoreline of a lake or inlet? Your environment plays a large role in choosing the best vest, with some certified for use inshore only. PFDs designed and engineered for offshore environments typically offer higher buoyancy to keep the wearer higher up out of the water in case of a delayed rescue (should one be required).
You may choose a higher amount of buoyancy because it feels safest. You may choose to go with the most minimal PFD that you can to optimize your comfort (while staying within the guidelines of your local transport or Coast Guard bodies). This guide to PFD Types can give you a sense of safety ratings by Type and environments they’re designed to perform in.
When it comes down to it, the best PFD is the one you wear.
A Smarter Way to Stay Safe
Understanding how to select the best life jacket could mean the difference between safety and risk. Prioritize quality, fit, and suitability to your activity. No swimmers should select PFDs specifically designed to provide maximum flotation and safety.
Remember, water safety isn’t just a precaution; it’s a responsibility.
With every life vest, Mustang Survival engineers look to balance safety with comfort, offering the peace of mind that your PFD will keep you afloat, making products that can perform in the most grueling environments while staying out of the way, and having you nearly forget you’re wearing one.
Find the Right PFD for Your Next Adventure
Whether you're casting lines, navigating whitewater, or heading offshore, understanding buoyancy helps you choose the right level of protection for your environment and activity. With decades of experience and a reputation for innovation, Mustang Survival designs every PFD to meet the highest standards of safety, comfort, and performance.
Explore the full line of USCG- and Transport Canada-approved PFDs—including foam, inflatable, and hybrid options—built for every adventure and every body.
