What Thickness Wetsuit Do You Need in the UK? 3/2, 4/3 and 5/4mm Explained

Buy a wetsuit that is too thin and your session ends early. Buy one that is too thick and you spend the summer overheating, with stiff shoulders every time you paddle. The thickness is the single biggest decision, and it comes down to one number: how cold the sea actually is where you go in.

How to read a wetsuit thickness: what 3/2 and 4/3 mean

Wetsuit thickness is quoted in millimetres of neoprene. A single number, such as 3mm, means the whole suit is that thick. Two numbers, such as 4/3mm, mean the torso is 4mm and the arms and legs are 3mm. Three numbers, such as 5/4/3mm, add a third zone, usually 5mm on the body, 4mm on the legs and 3mm on the arms.

The torso gets the thicker panels because that is where your core is, and the limbs get thinner neoprene so you can still paddle, kick and move. That is why a 4/3 is only one millimetre thinner on the arms but feels noticeably more flexible than a full 4mm suit.

Wetsuit thickness by water temperature

There is no official standard, so every brand publishes its own chart, and the figures vary by a degree or two. The table below follows the chart published by Vissla, one of the surf brands we stock, converted to Celsius. Treat it as a starting point rather than a rule.

What that means for UK sea temperatures

UK seas are colder than most people expect and they lag behind the air. Sea temperature peaks in late August and early September, weeks after the hottest air temperatures, and bottoms out in late winter. As a rough guide, the sea around the UK sits at about 5 to 10°C in winter and 15 to 18°C at the late-summer peak in the south, with Scotland and the North Sea colder than the south coast and the west. For the exact figure at your beach, check a local sea temperature reading on the day, because a few degrees changes which row of the table you fall into.

Put the two together and a practical UK pattern emerges:

• Late summer, southern beaches: a 3/2mm full suit covers the warmest weeks. A 2mm spring suit is only comfortable on the very warmest days, because the 19°C it is designed for is rarely reached in UK waters.
• Spring and autumn: this is 4/3mm territory for most of the country. The sea is still in the low teens even when the weather feels mild.
• Winter: a 5/4mm suit is the usual choice around 7 to 10°C, stepping up to a hooded 5/4/3mm or 6/5mm when the water drops below that.

If you only want one suit for the whole year, a 4/3mm is the most common compromise. It is a little warm in August and a little thin in January, and you fill the gaps with accessories.

Boots, gloves and hoods change the number

Accessories let you wear a thinner suit for longer. The same brand chart suggests boots once the water falls below about 11°C, gloves from about 10°C, and a hood below roughly 7 to 9°C, because the head, hands and feet are where most people feel the cold first. In practice that means a 4/3mm suit with 3mm boots can feel better than a 5/4mm with bare feet, and you keep the flexibility in the body.

Boot thickness follows the same logic as the suit. 3mm is the usual spring and autumn choice, 5mm suits colder months, and 7mm is for the coldest water. Gloves and hoods come in similar steps. If you are building a winter kit, our range of wetsuit boots, gloves and hoods runs from 1.5mm gloves up to 7mm boots, so you can match each piece to the temperature rather than overbuying across the board.

Seams matter as much as thickness

Two suits of the same thickness can feel very different in cold water because of how the panels are joined. Flatlock stitching lets water seep through the seams, so it only suits warm-water and summer suits. Glued and blind-stitched (GBS) seams are the standard on most 3/2mm suits. For 4/3mm and thicker, look for sealed or taped seams, which block the cold-water flushing that makes a stitched seam feel colder than the neoprene itself.

The product title usually tells you the thickness, and the description should say how the seams are finished. If it does not, ask before you buy.

Fit: why a wetsuit should feel tight on dry land

A wetsuit works by trapping a thin layer of water against your skin and letting your body warm it. A loose suit lets that layer flush out with every wave, and the suit feels thin however many millimetres it has. Aim for snug everywhere, with no gaps at the lower back, chest or crotch, and enough give in the shoulders that you can still reach forward and paddle.

Size from the brand's own chart rather than your high street size, and note that men's, women's and boys' suits are cut differently. Our wetsuit collection includes men's and women's full suits, spring suits and neoprene jackets, in thicknesses from 1mm to 6/5mm.

When to go one step thicker

The chart assumes an active surfer who is moving most of the time. Go up a step if you feel the cold easily, if you will spend long periods sitting still on a board or paddleboard, or if it is windy, because wind chill on wet neoprene makes the same water temperature feel colder. Go down a step if you are mostly swimming hard or you tend to overheat. A thicker suit is not automatically better: a 6/5mm in 16°C water is stiff, tiring to paddle in and uncomfortably warm.

A wetsuit also does not make cold water safe in its own right. Check the conditions, tell someone where you are going, and read the RNLI's beach safety advice before you enter the sea in any season.

A quick decision guide

Check the sea temperature at your beach, find the matching row in the table, then add boots, gloves or a hood if the water is under about 11°C. If you are somewhere between two rows, choose the thinner suit with accessories if you value movement, or the thicker one if you value warmth. If you are still building your kit, our surf shop brings the suits, boots, gloves and accessories together in one place.