Wetsuit temperature chart and thickness guide

Wetsuit temperature chart

This is the chart we show on the Water temperature page for every coastal place, with today’s row highlighted. It’s meant for surfing, bodyboarding and swimming:

Water	Wetsuit	How it feels
Below 52°F (11°C)	6/5 mm with hood, booties and gloves	Very cold: full kit only
52–57°F (11–14°C)	5/4 mm with booties	Cold: takes your breath away
57–63°F (14–17°C)	4/3 mm	Cool
63–66°F (17–19°C)	3/2 mm	Mild
66–72°F (19–22°C)	Shorty (springsuit)	Pleasant
72–75°F (22–24°C)	Rash guard or neoprene top	Very pleasant
Above 75°F (24°C)	No wetsuit	Warm

It’s a rough guide. If you feel the cold, plan to be in for more than an hour or there’s wind, go up one row. And if you’re torn between two suits, pick the thicker one: it’s easier to put up with being a bit warm than to warm back up in the water.

What the numbers mean: 3/2, 4/3, 5/4

Neoprene is rubber foam full of tiny gas bubbles, and those bubbles are what keep the cold out. Thickness is measured in millimeters, and most suits carry two numbers:

the first is the torso, where holding heat matters most;
the second is the arms and legs, thinner so you can paddle and swim without tiring.

A 4/3 is 4 mm on the chest and back and 3 mm on the arms and legs. A 3/2 is a spring and fall suit in Southern California; a 5/4 or 6/5 is a winter suit for cold water.

A wetsuit doesn’t keep you dry. It lets in a thin layer of water, your body warms it, and the suit stops it from being flushed out. That’s why fit matters as much as thickness. If the suit is loose, cold water pours in at the neck, wrists and ankles every time you move, and a thick suit ends up as warm as a thin one.

Beyond full suits, there are other pieces:

Rash guard or neoprene top: sun and chafe protection with a little warmth.
Shorty, or springsuit: short arms and legs, for mild water.
Booties, hood and gloves: in cold water your hands and feet go numb fast and your head is always exposed. In the chart, booties come in below 57°F (14°C), and hood and gloves below 52°F (11°C).

It’s not just the water: air, wind and time

The most common mistake is going by the air temperature. An 85°F day with 60°F water is still a 4/3 day. The National Weather Service puts it simply: dress for the water temperature, not the air temperature. Water pulls heat from your body far faster than air does, up to 25 times faster than air at the same temperature, according to the National Weather Service.

A few other things change the choice:

Wind. Whenever you’re out of the water, sitting on your board, on the boat between dives or in a kayak, wind chills a wet suit. On windy days, go up a row.
Time in the water. A three-hour surf session or two dives in a row will chill you much more than a 20-minute swim.
You. People who are lean, tired or not used to cold water lose heat sooner.

Surfing, diving, swimming and paddling

Surfing and bodyboarding

The chart above is built for surfing: you paddle constantly and spend a lot of time half out of the water, so the suit has to let your shoulders move.

Scuba diving

Divers need noticeably more insulation, for three reasons. You move very little, you stay in for 40 minutes to an hour, and, above all, neoprene compresses at depth: water pressure squeezes the gas bubbles, so the suit gets thinner and insulates less. On top of that, in summer the water at depth is often several degrees colder than at the surface. This is the chart we use on the Diving tab:

Water	Suit for diving
Below 50°F (10°C)	Drysuit
50–57°F (10–14°C)	7 mm semi-dry
57–64°F (14–18°C)	7 mm wetsuit
64–72°F (18–22°C)	5 mm wetsuit
72–79°F (22–26°C)	3 mm wetsuit
Above 79°F (26°C)	Shorty or rash guard

Below 64°F (18°C) the tab adds a hood and booties, and below 57°F (14°C), gloves too. A semi-dry seals better at the neck, wrists and ankles so very little water gets in, and a drysuit keeps water out entirely, with warm layers underneath. For when to dive, see our guide to diving and tides.

Open water swimming

Swim wetsuits are very flexible in the shoulders and add buoyancy. In World Aquatics competitions, wetsuits are mandatory when the water is below 64°F (18°C), and races aren’t held below 61°F (16°C). A World Aquatics-backed study of trained swimmers found that some could no longer maintain their core temperature at 60°F (15.5°C), just under that limit. Triathlons and local swims set their own rules, so check before you sign up.

Kayaking, paddleboarding and small boats

You don’t plan to get wet, but if you capsize you’re suddenly in the water. Dress for the fall, not the paddle. The US Coast Guard warns that water below 70°F (21°C) quickly lowers your body temperature and leads to hypothermia, and advises dressing for the water temperature, for example in a wetsuit or drysuit. And always wear a life jacket: the National Weather Service says it significantly increases your chances of survival.

Cold water shock and hypothermia

When you hit cold water suddenly, your body reacts before you can think. The RNLI, the UK and Ireland’s lifeboat service, says cold water shock can set in below 59°F (15°C): you lose control of your breathing and movement, and your heart rate and blood pressure shoot up, which can lead to cardiac arrest. The National Weather Service adds that cold shock can be just as severe in 50–60°F (10–15°C) water as at 35°F (2°C), and that the gasp reflex can be triggered in water as warm as 77°F (25°C).

Two more problems follow. Your arms and legs start losing strength as soon as you’re in, and it gets worse the longer you stay, until swimming or holding on becomes hard. Later comes hypothermia, when your core temperature drops to 95°F (35°C).

If you fall into cold water, the RNLI’s advice is to Float to Live:

Don’t try to swim straight away. The initial effects pass in less than a minute.
Tilt your head back, with your ears in the water.
Relax and control your breathing.
Gently move your hands and legs to stay afloat, and spread your arms and legs for stability. It’s fine if your legs sink.
Once your breathing is under control, call for help or swim to safety.

If you can’t get out, the National Weather Service says to stay calm, conserve energy and get as much of your body out of the water as you can, for example onto something that floats. While you wait for rescue, draw your knees to your chin with your legs together, press your arms against your sides and keep your head out of the water. If there are several of you, huddle together to keep warm.

If you pull someone out of cold water, follow the Red Cross steps the National Weather Service lists: call 911, move the person gently to a warm place, monitor breathing and give CPR if needed, remove wet clothing and wrap them in blankets or dry clothes. Warm them slowly, core first, not hands and feet. Don’t put them in warm water: rapid warming can cause dangerous heart rhythms. On the water, the US Coast Guard monitors VHF channel 16.

How the water changes through the year

The ocean takes a long time to warm up and cool down, so it lags behind the air. These are NOAA’s 1991–2020 averages, the normals we show on the Water temperature page for each place:

Place	February	May	August	November
Bar Harbor, Maine	39°F (4°C)	44°F (7°C)	55°F (13°C)	49°F (10°C)
Cape Cod (Provincetown), Mass.	40°F (4°C)	49°F (10°C)	67°F (19°C)	51°F (10°C)
Outer Banks (Nags Head), N.C.	46°F (8°C)	64°F (18°C)	78°F (26°C)	61°F (16°C)
Miami Beach, Fla.	76°F (25°C)	81°F (27°C)	85°F (30°C)	80°F (27°C)
Galveston, Texas	59°F (15°C)	78°F (25°C)	86°F (30°C)	69°F (21°C)
Monterey, Calif.	55°F (13°C)	54°F (12°C)	58°F (14°C)	57°F (14°C)
La Jolla, Calif.	59°F (15°C)	64°F (18°C)	70°F (21°C)	64°F (18°C)
Honolulu, Hawaii	75°F (24°C)	77°F (25°C)	80°F (27°C)	79°F (26°C)

Read with the wetsuit chart in hand:

Maine stays cold all year: even in August, Bar Harbor calls for a 5/4 with booties, and winter means a 6/5 with hood and gloves.
The Outer Banks and the Gulf Coast swing the most, from a full suit in winter to no wetsuit in summer.
Northern and Central California barely change. In Monterey the water is coldest in spring, when northwest winds bring cold water up from below, and a 4/3 or 5/4 works year-round.
Southern California runs from a 4/3 in winter to a shorty in late summer at La Jolla.
South Florida and Hawaii are warm all year: at Miami Beach you rarely need more than a rash guard, even in winter.

For comparison, the RNLI puts the average sea temperature around the UK and Ireland at just 54°F (12°C). These are averages for the open sea: any given year can run warmer or colder, which is why each page also tells you whether today’s water is above or below normal.

Where TidePlanet’s water temperature comes from

The Water temperature tab for each coastal place shows several numbers, and they don’t all come from the same source:

The water right now and over the next few days is the sea surface temperature from an ocean model run by Copernicus Marine, the European marine service, which reaches us through Open-Meteo. It isn’t a thermometer in the water: it’s a model that’s corrected every day with ocean observations, on a grid about 5 miles (8 km) across. Each place uses the nearest grid cell, and the page tells you how far away it is.
The last 60 days come from the same model, shown on a chart along with the outlook for the coming weeks versus normal.
The monthly normals are 1991–2020 averages from NOAA OISST, which blends satellite, ship, buoy and Argo float measurements on a quarter-degree grid. We use them to tell you whether today’s water is warmer or colder than normal and when the best months to swim are.
The wetsuit chart, with today’s row highlighted.
The nearest buoy. On each place’s main page, if there’s a buoy or marine station within about 37 miles (60 km), you’ll see its latest real reading: waves, wind and, if it measures it, the water temperature. In Monterey, for example, that’s a Scripps CDIP buoy offshore.

Two caveats. Right by the shore, in coves, bays and river mouths, the water can be a little colder or warmer than the model cell. And the number is for the surface: if you’re diving, expect it to be colder below.

In short

Choose your wetsuit by the water temperature, not the air temperature.
The first number is the thickness of the torso and the second the arms and legs, in millimeters.
Divers need a thicker suit than surfers, because neoprene compresses at depth and you move less.
Below about 59°F (15°C), cold water shock can take your breath away. Don't try to swim right away; float until your breathing settles.
The ocean lags the air. Water is usually warmest in August or September and coldest in February or March.
On TidePlanet, today's water comes from an ocean model and the monthly normals from NOAA's 1991–2020 averages.

Frequently asked questions

What wetsuit do I need for 60-degree water?

For surfing or swimming in 60°F (16°C) water, a 4/3, which covers 57 to 63°F (14 to 17°C). For diving, a 7 mm wetsuit, because you move less and neoprene compresses at depth. If it's windy or you'll be in for a long session, go thicker.

At what water temperature do you not need a wetsuit?

For a normal swim or surf session, above about 75°F (24°C). Between 72 and 75°F (22 to 24°C), a rash guard or a neoprene top is enough. Even so, the National Weather Service notes that the cold shock gasp can be triggered in water as warm as 77°F (25°C), and on a long swim you'll cool down even in water that feels fine.

What does 4/3 mean on a wetsuit?

It means the neoprene is 4 millimeters thick on the torso and 3 millimeters on the arms and legs. The torso is thicker to hold heat where it matters most, and the arms and legs are thinner so you can paddle and swim more easily.

What is cold water shock?

It's the body's reaction to sudden immersion in cold water. The RNLI, the UK and Ireland's lifeboat service, says it can happen below 15°C (59°F). You lose control of your breathing, your heart rate and blood pressure jump, and you can inhale water. The RNLI says the initial effects pass in less than a minute, so don't try to swim right away; float until your breathing settles.

What is considered cold water?

There's no single official line. The US Coast Guard warns that water below 70°F (21°C) will quickly lower your body temperature and lead to hypothermia, and advises dressing for the water temperature, for example in a wetsuit or drysuit. The RNLI says cold water shock can set in below 59°F (15°C).

Why is the water colder than the forecast says?

Forecasts give the temperature at the sea surface over grid cells several miles across. Right by the shore, in coves, bays and river mouths, the water can be a little colder or warmer, and a few feet down it's often colder, especially in summer.

Water temperature and wetsuits: what thickness do you need?