Triathlon Hydration & Electrolyte Calculator

Why Hydration Matters in Triathlon

Dehydration is one of the leading causes of DNF (Did Not Finish) in endurance races. Losing just 2% of your body weight in fluid can reduce performance by up to 10–20%. During an Ironman, athletes can lose 1–2.5 litres of sweat per hour depending on conditions — making a solid hydration plan non-negotiable.

How Sweat Rate Works

Your sweat rate depends on body weight, exercise intensity, temperature, humidity, and acclimatization. The gold standard is a sweat test: weigh yourself before and after a 1-hour workout (without drinking), and the difference in grams equals your sweat rate in ml/hr. Our calculator estimates this if you don't have a measured value.

Common Hydration Mistakes

Overhydration (hyponatremia) — drinking too much plain water dilutes sodium, causing nausea, confusion, and in severe cases, medical emergencies.
Waiting until thirsty — by the time you feel thirsty during a race, you're already 1–2% dehydrated.
Ignoring the run leg — many athletes hydrate well on the bike but forget to adapt their strategy for running, where stomach tolerance is lower.
Skipping electrolytes — water alone doesn't replace the sodium lost through sweat, especially in hot conditions.
Not practising in training — your race day plan should be tested during long training sessions first.

Hydration by Race Distance

Sprint Triathlon: A shorter event (~1.5 hours), so pre-race hydration matters most. Carry one bottle on the bike and use aid stations on the run.

Olympic Triathlon: At ~3 hours, you need a deliberate bike hydration strategy. Aim for 500–750ml per hour on the bike.

Half Ironman (70.3): With 5–7 hours of racing, sodium losses become significant. Plan for 2–4 bottles on the bike plus electrolyte tabs or salt capsules.

Full Ironman: Races lasting 10–17 hours require meticulous planning. Dehydration and hyponatremia are real risks. Use a mix of sports drink and water, and consume 500–1000mg sodium per hour depending on conditions.

FAQ

How much water should I drink during an Ironman?

Most athletes need 600–1000ml per hour, depending on heat and sweat rate. Use this calculator to get a personalized estimate based on your body weight and race conditions.

Can you drink too much water during a triathlon?

Yes. Overhydration (hyponatremia) is dangerous. Always include electrolytes with your fluid intake, and don’t exceed ~1.2L per hour unless you have a measured high sweat rate.

How many electrolyte tablets do I need for a half Ironman?

Typically 8–15 servings across 5–7 hours, depending on sodium content per tab. This calculator gives you a specific number based on your inputs.

Should I drink during the swim in a triathlon?

No — focus on pre-loading with 400–600ml of fluid 60–90 minutes before the race starts. You can’t practically drink during the swim leg.

What’s better: water or sports drink during a race?

A mix of both. Sports drinks provide sodium and carbs, but plain water helps with cooling. Aim for 50–70% sports drink and the rest water.