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For a sprint triathlon, most people wear one outfit for the whole race: a tri suit, or a swimsuit with shorts added after the swim. In open water you add a wetsuit when the water is cold. For the bike you need a helmet and shoes, and for the run your usual trainers. What to wear for a triathlon depends on pool or open water, the weather and what you already own.
This guide goes leg by leg, then gives a full kit checklist in the order you use it. We have not tested any kit. Rules quoted are from British Triathlon's Competition Rules 2026 unless we label them as World Triathlon rules.
The basic idea: one outfit, small changes
A triathlon has three legs and two transitions. T1 is the change from swim to bike, and T2 is the change from bike to run. Every item you take off or put on in transition costs time, so the simplest plan is one base layer that works for all three legs, with a few additions:
- Swim: base layer, plus goggles, cap and a wetsuit if needed.
- T1: remove wetsuit, cap and goggles; put on helmet, then shoes and sunglasses if you use them.
- Bike: base layer, helmet, shoes.
- T2: rack the bike, take off the helmet, change shoes if you rode in cycling shoes.
- Run: base layer, trainers, race number, cap or visor if sunny.
Never wear anything new on race day. Try every item in training, including in a brick workout, where you ride and then run straight away.
What to wear for the swim
Pool triathlon
Many first races have a pool swim. British Triathlon's Appendix A gives the pool sprint swim as 400 m, and some club races use a slightly different length: the Thames Turbo Sprint Triathlon in Hampton listed a 432 m pool swim for its 2026 race. Wetsuits are not used in a pool. Wear a tri suit, or a swimsuit or trunks, plus goggles and a swim cap, using the race cap if the organiser provides one.
Open water triathlon
The open water sprint swim is 750 m. Under British Triathlon rule 4.2, a wetsuit is mandatory when the water is below 15.9 °C. It is forbidden above 22 °C for swims up to 1500 m if you are 59 or younger (age on 31 December), and above 24.6 °C in other cases. The rules recommend that novices and age-groupers up to 59 wear one up to 22 °C. The temperature is taken one hour before the start, so you may not know for sure until race morning. Bring the wetsuit either way.
Under the wetsuit, wear your tri suit or swimsuit. You keep it on for the rest of the race. See our triathlon wetsuit guide for fit and hire, and the tow float and goggles guide for training swims and lens choice.
What to wear for the bike
You ride in the same base layer. A tri suit has a thin pad for the saddle. If you swam in a swimsuit, pull on cycling shorts in T1.
- Helmet: essential. Under World Triathlon rules (section 5.2(g)) the helmet must be approved by a nationally accredited testing authority and worn for all riding, and the chin strap must be fastened before you take the bike off the rack and stay fastened until the bike is racked again. British Triathlon events have their own rules, so check the race briefing, but expect the same habit: helmet on and done up before you touch the bike.
- Shoes: running trainers with flat pedals are fine for a first sprint. Clip-in cycling shoes need practice.
- Sunglasses: useful against grit and glare.
- Top layer: in cool weather, a gilet or arm warmers. Wet skin makes tight layers hard to pull on, so choose something loose.
What to wear for the run
Keep the same base layer, swap to trainers if you rode in cycling shoes, and clip on your race number. Elastic laces save time tying shoes in T2. Many athletes use a race belt, an elastic band with your number on it, so the number can face backwards on the bike and forwards on the run without pinning it to your suit. Check the race information for where the number must be worn. Add a cap or visor on a sunny day.
What to wear in cold weather
UK race seasons include cold mornings. British Triathlon's rule 4.4 sets limits for cold water: below 11 °C there is no open water swim in competition, and the maximum swim distance is shortened to 1000 m at 13 °C, 600 m at 12 °C and 300 m at 11 °C. For the swim, a wetsuit is mandatory below 15.9 °C, and a second silicone cap under the race cap helps keep your head warm. For the bike, the first minutes after a cold swim feel coldest: a gilet, arm warmers or a light jacket, plus gloves if you can get them on with wet hands. On the run you usually warm up fast, so the base layer is often enough.
Practical points for women and men
- Women: some tri suits have a built-in shelf bra. If you need more support, wear a sports bra under the suit, and test it in the water and on a long run, as wet straps can rub. Women's-cut suits and wetsuits are sized differently to men's, so use the brand's women's chart.
- Men: a tri suit or tri shorts is worn without underwear, as you would wear cycling shorts. Body glide or anti-chafe balm on the neck helps with wetsuit rubbing.
- Everyone: put anti-chafe balm on any spot that rubs in training. A small pin or toilet stop is easier in a two-piece suit.
Read our tri suit guide for one-piece and two-piece options, pads and sizing.
See triathlon kit at Decathlon
Transition rules
Transition rules differ by event, so listen to the briefing. The detail below is from the World Triathlon Competition Rules (section 7), which apply at World Triathlon events, not necessarily at British Triathlon events in the UK:
- Equipment stays within 0.5 m of your bike or box.
- Only equipment you use in the race may be left in transition.
- No marking your position with towels or marks; these are removed.
- The wetsuit is fully removed only in the designated area or at your transition spot.
Even where the rules are different, a small, tidy space is quicker. Lay kit out in the order you will use it. Our guide to British Triathlon rules covers the rules we have verified for UK races.
Triathlon kit checklist, in transition order
| Stage | Item | Notes |
|---|---|---|
| Swim | Tri suit, or swimsuit or trunks | Worn all race |
| Swim | Wetsuit (open water) | Mandatory below 15.9 °C under British Triathlon rules |
| Swim | Goggles, plus a spare pair | Clear or tinted to suit the light |
| Swim | Race cap | Check whether the organiser provides one; own silicone cap under it if cold |
| Swim | Anti-chafe balm | Neck and underarms under a wetsuit |
| T1 | Small towel | To stand on and dry feet; not to mark your spot where that is banned |
| T1 | Helmet | On and fastened before you take the bike |
| T1 | Sunglasses | Put in the helmet so you do not forget them |
| T1 | Cycling shorts or top | Only if you swam without a tri suit |
| Bike | Bike, checked | Tyres pumped, brakes working |
| Bike | Cycling shoes or trainers | Use what you trained in |
| Bike | Bottle with drink | In a cage on the bike |
| Bike | Gilet or arm warmers | Cold days only |
| T2 | Trainers with elastic laces | Saves tying |
| T2 | Race belt with number | Check where the number must be worn |
| Run | Cap or visor | Sun or rain |
| Run | Watch | Optional |
| After | Warm dry clothes and shoes | You cool down fast after finishing |
| After | Bag for wet kit | Wetsuit and tri suit |
Pack the night before, using this list, and lay it out in the same order at home once to check nothing is missing. For a full picture of your first race, read our triathlon for beginners guide.
Frequently asked questions
What should I wear for my first triathlon?
Wear one outfit you can swim, ride and run in: a tri suit, or a swimsuit or trunks with cycling shorts or running shorts. Add a wetsuit if the swim is in open water below 15.9 °C, which British Triathlon makes mandatory. On the bike you need a helmet. For the run, trainers you already use. Do not race in anything new.
Can I wear a normal swimsuit for a triathlon?
Yes, especially for a pool triathlon. A swimsuit or trunks is fine for the swim. You can then pull on cycling shorts or running shorts and a top in transition, which takes a little longer but is perfectly normal at a first race. If you plan to do more races, a tri suit saves the change and is designed to be worn all day.
Do I need cycling shoes for a sprint triathlon?
No. Many first-timers ride in their running trainers with flat pedals, which means one less change in T2. Clip-in cycling shoes are more efficient on the bike but need practice, both clipping in and running in them through transition. If you have not trained in them, wear your trainers on race day and decide later.
What do I wear for a triathlon in cold weather?
In open water below 15.9 °C a wetsuit is mandatory in British Triathlon races, and a second silicone cap under the race cap helps keep your head warm. On the bike add a gilet or arm warmers and gloves you can put on with wet hands. Practise putting them on quickly, as wet skin makes every layer harder to pull on.
Sources
- British Triathlon Competition Rules 2026 (April 2026), rules 4.2 and 4.4 and Appendix A, checked 6 October 2026
- World Triathlon Competition Rules 2026, sections 5.2(g) and 7, checked 6 October 2026
- Thames Turbo Triathlon Club: our races, checked 6 October 2026
- Better: West Reservoir Centre open water swimming, checked 6 October 2026