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Choosing a 170N or 275N Lifejacket

24 Oct 2023
Choosing between our 170N and 275N lifejacket is one of the most popular conversations we have at boat shows, in stores, or via Pro Support.

Life jackets around the world are certified to ISO, which is the International standard for personal flotation devices and life jackets. The two main ISO certificates for lifejackets are 150N or 275N buoyancy.

The ISO standard allows manufacturers like Spinlock to provide higher levels of support to the levels 150N or 275N, so with the research and the development we undertake we have developed an inflatable lifejacket bladder in our products which is 170N of buoyancy and this passes, in fact, surpasses, the 150N standard.


170N (150N) is the accepted standard for recreational sailing. It is a comfortable, wearable size that is not too intrusive, and it provides significant buoyancy when in the water. The bladder is designed to float the user at a certain angle and height above the water.

Many offshore and ocean sailors such as The Ocean Race sailors and The Clipper Race choose to wear 170N as this provides enough buoyancy without the addition of bulk and heaviness when wearing for long periods of time.


The 275N provides significantly more buoyancy so is suitable for situations where additional weight might be carried, i.e., toolbelt, steel toecap boots, weapons, etc.  The additional buoyancy and size is not always an advantage as the lifejacket is bulkier and heavier to wear and harder to use in the water, i.e., if entering a life raft, etc. 

If you have participated in a sea survival course or have inflated and used a lifejacket to test it out then you may have experienced that a 275N is more difficult to swim in and to gain entry to a life raft. 

We recommend that unless you really need one, that the 170N is suitable for most people. The Ocean Race and The Clipper Race both wear 170N lifejackets when sailing around the world!

Some frequently asked questions:

What is N and buoyancy?

The N stands for Newtons. A newton is the unit of measure for force. The more newtons the more buoyancy.

Do life jackets have a weight limit?

We are often asked how much weight can a life jacket hold or if there is a weight limit for life jackets?

If this is a question relating to the size and shape of a person, then no there is no weight limit. The more mass a person has, the easier they are to float.

If the question relates to a person with a tool belt, steel toe cap boot or heavy tools, then this extra weight may mean a 275N life jacket is more suitable.

How much buoyancy does a child need?

The Spinlock Deckvest CENTO is our child’s automatic lifejacket and it is tested to the 150N ISO standard, however, it is scaled down accordingly and is an actual buoyancy of 100N. The Deckvest NEMO+ is the newest Spinlock lifejacket and comes in two sizes, up to 15kg (Infant) and 15-30kg (Child). The Deckvest NEMO+ is tested to the 150N ISO standard and has been scaled down to: Infant 45N and Child 60N.


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