Lifejacket buoyancy is measured in Newtons (N). Ten Newtons equals 1kg of flotation. All lifejackets must carry the CE or ISO mark.
Newton ratings are relative to the weight of the intended user. Make sure the lifejacket you choose is the correct size for you and that it has the right Newton rating for your weight. A 150N lifejacket designed for a child or young adult will not sufficiently float an adult. If you are buying for an adult you must get a 150N lifejacket designed for an adult's weight.
There are four European (CE) and now International (ISO) standards for lifejackets and buoyancy aids:
Buoyancy aid (50N)
The 50N personal flotation device (PFD) is currently called a buoyancy aid. It is intended for use by those who are competent swimmers and who are near to the bank or shore, or who have help and means of rescue close at hand. These PFDs have minimum bulk, but they are of limited use in disturbed water and cannot be expected to keep the user safe for a long period of time. They do not have sufficient buoyancy to protect people who are unable to help themselves. They require active participation by the user.
Recommended for dinghy sailors, windsurfers, water skiers, and personal watercraft where the user might reasonably expect to end up in the water.
The 100N lifejacket is intended for those who may have to wait for rescue but are likely to do so in sheltered and calm water. Whilst these lifejackets are less bulky than those with more buoyancy, they are intended for use in relatively sheltered waters. They may not have sufficient buoyancy to protect people who are unable to help themselves and may not roll an unconscious person onto their back particularly if they are wearing heavy clothing.
The 150N lifejacket is intended for general offshore and rough weather use where a high standard of performance is required. It should turn an unconscious person into a safe position and requires no subsequent action by the wearer to keep their face out of the water. Its performance may be affected if the user is wearing heavy and /or waterproof clothing. Recommended for general use on coastal and inshore waters when sailing, fishing, etc, where the user would not expect to end up in the water.
The 275N lifejacket is intended primarily for offshore and extreme conditions and for those wearing heavy protective clothing that may adversely affect the self righting capacity of the lifejacket. This lifejacket is designed to ensure that the wearer of floating in the correct position with their mouth and nose clear of the surface of the water. Recommended for offshore cruising, fishing and commercial users.