Wetsuit Thickness Calculator

How it works

Effective temp = water temp − wind adjustment (up to 3 °C) − cold-sensitivity (±2 °C) + activity (swim +3, paddle +1, dive −2) − 1 if over 2 h; map to thickness bands

Neoprene keeps you warm by trapping a thin layer of water and insulating it, and the thickness needed rises steadily as water temperature falls — from a shorty in tropical water to 6 mm and a hood at single-digit temperatures, beyond which a drysuit is safer. Water alone is not the whole story: wind chills a wet surfer far faster than still air, swimmers generate their own heat and need mobility more than millimetres, and divers lose warmth to still water that gets colder with depth while their suit compresses and insulates less. Personal metabolism matters enormously, which is why two people in the same line-up wear different suits. Extremities lose heat fastest, so boots, gloves and a hood often extend the season more effectively than a thicker suit.

Worked example

15 °C water, breezy, an average surfer for a 90-minute session: a 4/3 mm full suit with 3 mm boots. The same water for an open-water swimmer reads as 18 °C effective — a 3/2 or swim-specific 3 mm suit.

Frequently asked questions