Buoyancy explained: what a newton rating means for a wearer

Guide · 28 September 2026 · Figures reviewed 6 October 2026

Life jackets are rated in newtons, which reads like an engineering figure until it is put beside a person. This guide gives the conversion, explains why the number is so much smaller than a body weight, and shows how MM lists buoyancy against user weight across the range.

From newtons to kilograms

A newton is a unit of force. Gravity pulls on one kilogram with a force of about 9.8 N, so 10 N of buoyancy holds up roughly one kilogram in water. A 150 N jacket therefore provides about 15 kg of lift, and a 240 N jacket about 24 kg.

Why that is enough

A human body is almost neutrally buoyant, so it needs only a few kilograms of extra lift to float. The jacket’s job is to provide that lift where it is needed: holding the airway clear of the water, supporting waterlogged clothing and any equipment, and, in the higher classes, turning an unconscious wearer face-up. Higher buoyancy buys more of each of those, which is why offshore and heavily equipped crews are specified upward.

Buoyancy against user weight

MM lists most jackets with a maximum user weight as well as a buoyancy. Read the two together: the buoyancy is the lift the jacket gives, and the user weight is the wearer it was designed and tested around. The table below is drawn from the catalogue data.

Figures are as listed in MM’s catalogue data; standards named are as stated by MM Techno Plast. For the PFD type names in the table, see PFD types explained.