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When you next pick up your lifejacket or buoyancy aid, look and see what Newtons it has. It could be anything from 50N up to 305N with anything in between. Do you know what the number represents?

All lifejackets/buoyancy aids must comply to one of four ISO 12402 standards, these are as follows.


50N – PART 5

Buoyancy aids as standard come with a 50N rating. They are designed to be worn during surface watersports, when there is a high chance you will find yourself in the water at some point in time – dinghy sailing, kayaking, canoeing, SUP. These lifejackets that have a carrying capacity of 50 Newtons, they are officially buoyancy aids, have a slightly simpler design than lifejackets. A 50N buoyancy aid keeps you afloat but lacks a collar to support your head. It has the buoyancy force more evenly distributed between the front and back and therefore does not guarantee to turn an unconscious person to a supine position. A 50N buoyancy aid is therefore recommended for swimmers who weight at least 25kg.

A buoyancy/lifejacket with Newtons up to 99.9N is rated at 50N.

100N – PART 4

These are generally inherent buoyant foam lifejackets; a range of inflatable ones are available. They are for children and as with all lifejackets they will turn you onto your back should you find yourself unconscious face down in the water. Lifejackets are available with inflatable lung or with inherently buoyant material, common to all is that when inflated or in the water position they have most of the buoyancy force on the front and a sturdy collar that supports and holds up the head. A lifejacket is the obvious choice for people who cannot swim.

Lifejackets always have a carrying capacity of at least 100N. The inflatable models are divided into different classes depending on the conditions under which they are to be used. An automatic lifejacket inflates when the user ends up in the water, while a manual life jacket must be activated by the user.    

A lifejacket with Newtons up to 149.9N is rated to 100N.

150N – PART 3

This is the go-to lifejacket for those heading out on sheltered and coastal waters. Its most common use is for those going yachting, motorboating or out on a RIB. These are lifejackets, either on manual or auto-inflate, and will rotate you and keep you afloat in your clothing and sailing gear.

A lifejacket with Newtons up to 274.9N is rated to 150N.

275N – PART 2

Lifejackets in this category offer the greatest buoyancy. These are specialist lifejackets, predominantly for those offshore. If you wear lots of layers that ultimately equate to heavy clothing and/or you are heading offshore in potentially big seas, this is the lifejacket you should be wearing.

A lifejacket with Newtons greater than 275N is still rated as a 275N lifejacket.


Q: Does my weight depend on the buoyancy I require?

A: No. Just because you weigh more as a person does not mean you need more buoyancy. The lifejacket N you go for should be based on the type of activity you are doing.

Q: I brought a 165N should have just gone for a 150N?

A: No. Not necessarily.  Lifejacket manufactures have gotten into a number war. Customers see a higher number and think oh that must be better. Well yes it will offer great buoyancy however greater buoyancy is not always needed, and with greater buoyancy you need a bigger bladder (air pocket) and therefore the lifejacket can become bulky.

Rule of thumb.

  • A bigger number will always offer you more buoyancy, but it comes with drawbacks, as the bigger lifejackets are bulkier and can be more restrictive.
  • The N number represents the buoyancy, it is rated to the lower Part of the ISO 12402. i.e. a 165N is still rated as per a 150N.
  • The safest lifejacket is the one you wear.

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