Wetsuit calculator: should you wear one for this swim?

When is a wetsuit mandatory in a triathlon?

Under World Triathlon rules, a wetsuit is mandatory for age group athletes when the water is 15.9 degrees Celsius or colder, which is about 60.6 Fahrenheit. That rule exists for safety: cold water pulls heat out of you far faster than cold air, and a long swim in it without neoprene is dangerous. USA Triathlon takes a different approach and never makes a wetsuit mandatory at any temperature in its standard age group rules. In practice that difference matters less than it sounds, because at those temperatures almost everyone wears one anyway.

At what water temperature are wetsuits banned?

For World Triathlon age group races, wetsuits are forbidden at 22.0 degrees Celsius and above when the swim is 1500 meters or shorter, and at 24.6 degrees and above for longer swims. Athletes aged 60 and over keep the higher 24.6 degree limit at every distance. USA Triathlon draws its hard line at 84 degrees Fahrenheit, about 28.9 Celsius. The reasoning is the mirror image of the cold rule: a wetsuit traps heat, and racing hard inside one in warm water is a genuine overheating risk, not just a comfort problem.

What is the USAT 78 degree rule?

In USA Triathlon age group races you can wear a wetsuit with full award eligibility up to a water temperature of 78.0 degrees Fahrenheit, about 25.6 Celsius. From 78.1 to 83.9 degrees you are still allowed to wear one, but you give up your age group rankings and awards for that race. That middle band is USAT saying: if you need the suit for confidence or safety you may use it, but it counts as an aid once the water is warm enough that nobody needs it for warmth. If a podium matters to you, check the announced temperature before you zip up. Both rulebooks also cap wetsuit thickness at 5 millimeters.

Should I wear a wetsuit when it is optional?

For most triathletes, yes. The classic study on this compared swimmers and triathletes over a 400 meter time trial and found triathletes were about 19 seconds faster in a wetsuit, mostly because the suit lifts your hips and legs and cuts drag (Chatard et al., 1995). The benefit was much smaller for trained pool swimmers who already sit high in the water. I swam the 200 individual medley at two Olympic Games, always in pools kept at competition temperature, so I am exactly the kind of swimmer that study says gains the least, and I would still take the suit in cool open water: warmth and buoyancy buy you calm, and calm is worth more than seconds in a triathlon swim. If open water itself is the scary part, the suit helps, and so does knowing how to sight without breaking your stroke.

How do I find out the official water temperature?

At races run under World Triathlon rules, the head referee announces the official water temperature and the wetsuit decision one hour before the start. Local races usually announce it at the race briefing or on the event page the day before. Do not plan your race around the forecast alone: the measured temperature on the morning is what the rules are applied to, so pack for both outcomes and decide when the number is official.

What pace should I swim once the wetsuit question is settled?

A wetsuit changes what you wear, not how you should pace, and pacing is where most triathlon swims actually go wrong. Two short time trials in the pool give you a threshold number you can aim at on race day: run them through my swim pace calculator to get your Critical Swim Speed and five training zones, and read swim training zones explained for how to build the weeks before the race. And one thing the clock will never tell you: what your stroke is doing while you hold that pace. That is what I built SwimLytic for: film a lap and the app scores 8 technique metrics frame by frame, entirely on your phone.