Electrolyte Needs Calculator
Estimate your electrolyte requirements based on your body weight, activity duration, sweat rate, and environmental conditions.
How many electrolytes do triathletes need per hour?
Most triathletes need 500–1,000 mg of sodium per hour during racing, scaling to 1,500 mg+ for heavy sweaters in hot conditions. Potassium, magnesium and calcium follow standard ratios and are harder to under-dose. Sodium is the one that goes wrong on race day.
- Light sweaters in cool weather: 400–600 mg sodium/hr
- Moderate sweaters: 700–1,000 mg sodium/hr
- Heavy sweaters in heat: 1,200–1,500+ mg sodium/hr
- Pair with 500–1,000 ml fluid per hour — sodium alone dehydrates
Your Details
Enter your information to calculate personalized electrolyte recommendations
Example calculation
Athlete: 72 kg heavy sweater, 5-hour 70.3 race in hot weather (30°C).
Base: 1,000 mg sodium/hr × 1.3 (hot) = 1,300 mg/hr.
Total race sodium: 1,300 × 5 = 6,500 mg.
Fluid target: 900–1,200 ml/hr paired with that sodium.
Common mistakes
- Only counting sodium in drink mix — gels, salt caps and food all contribute
- Trusting a fizzy tab label (most are ~300 mg/tab — low for heavy sweaters)
- Over-hydrating with plain water — causes hyponatremia
- Not testing sodium strategy in training before race day
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How this calculator works
Hourly sodium need = baseline (light/moderate/heavy sweat) × temperature multiplier. Other electrolytes scale from sodium using sports-nutrition ratios.
Assumptions
- • Sweat sodium of 500 / 700 / 1000 mg/hour for light / moderate / heavy sweaters
- • Hot-condition multiplier of 1.3 over moderate temperature
- • Magnesium and calcium based on typical sports-nutrition guidance, not personalised lab values
Limitations
- • Genetic salty sweaters may need 1500 mg+/hour — test in training
- • Does not factor in altitude or humidity directly
- • Hyponatremia risk if you over-drink water without sodium — start lower and adjust up
Who this is for
- • Endurance athletes planning hot-weather training and racing
- • Heavy or salty sweaters who cramp on long sessions
- • Anyone testing a fuelling strategy before race day
Who this is not for
- • People with diagnosed kidney or heart conditions affecting sodium intake
- • Children — different fluid and electrolyte needs
Electrolyte Calculator FAQ
Scientific References
Analysis of sweat sodium losses and replacement strategies
Official position on hydration and electrolyte replacement
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