Electrolyte Replacement Calculator for Athletes
Calculate how much sodium, potassium, and fluid you need per hour of exercise based on body weight, duration, temperature, and intensity. Based on ACSM guidelines. Free, instant results.
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Reviewed by: Martín Rodríguez (editorial policy ) · Last reviewed:
Result
Recommended Sodium
1,000 mg sodium + 400 mg potassium + 1.5 L fluid
Potassium
Total Fluid
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For guidance only — not medical advice. Consult a licensed healthcare professional.
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When you exercise for more than 60–90 minutes, your body loses sodium, potassium, and water through sweat. Drinking only water without electrolytes causes dilutional hyponatremia — a medical emergency with nausea, seizures, and in extreme cases, fatal brain swelling. This calculator estimates your sodium, potassium, and fluid needs from the four most important variables: body weight, exercise duration, ambient temperature, and effort intensity.
When to use this calculator
- Marathon Runner in Hot Weather — A 70 kg runner races a road marathon (4.5 hours) in 28 °C heat at moderate-high intensity. The calculator estimates ~600–700 mg/hour of sodium, helping the runner plan salt capsules at each aid station to supplement a standard sports drink.
- IRONMAN Triathlete Pre-Race Planning — An 80 kg triathlete competing in a 10–11 hour IRONMAN uses the calculator to model bike and run segments at different intensities, revealing a total sodium need near 5,800 mg — far above what commercial sports drinks alone provide.
- Trail Ultramarathon with Temperature Swing — A 65 kg ultrarunner calculates separate estimates for cool overnight conditions and hot midday sections, discovering sodium needs nearly double in the heat phase (from ~380 mg/h to ~720 mg/h).
- Recreational Cyclist on a Century Ride — An 85 kg cyclist planning a 6-hour century ride finds that a single 500 mL bidon of plain water per hour falls far short of sodium needs, and adds a commercial electrolyte mix to every other bottle.
- CrossFit or HIIT Athlete with Daily Double Sessions — A 90 kg CrossFit athlete running two 1.5-hour sessions per day sees daily exercise sodium needs exceeding 2,400 mg — explaining persistent afternoon cramping despite feeling 'well-hydrated' from drinking plain water.
- Sports Dietitian Building a Client Protocol — A dietitian uses the calculator to create a baseline hydration protocol for a 58 kg soccer player competing in summer heat, then refines it with sweat testing data.
Sodium Content of Common Sports Hydration Products
| Product / Source | Sodium (mg/L equivalent) | Adequate for Events > 90 min? | Notes |
|---|---|---|---|
| Plain water | 0 mg/L | No — hyponatremia risk | Never sole source in prolonged exercise |
| Gatorade / Powerade (standard) | ~450 mg/L | Only for < 90 min | Too dilute for ultra-endurance |
| LMNT (1 sachet / 500 mL) | ~2,000 mg/L (1,000 mg per sachet) | Yes | High sodium; no sugar |
| Precision Hydration PH 1000 | ~1,000 mg/L | Yes | Isotonic; good for long events |
| Nuun Sport (1 tablet / 500 mL) | ~720 mg/L (360 mg per tablet) | Marginal (< 2 hrs) | Lower sodium than PH/LMNT |
| DIY (1 L water + 1 tsp table salt) | ~2,300 mg/L | Yes — adjust to taste | Cheapest option; add 30 g sugar if needed |
Fuente: American College of Sports Medicine (ACSM) Position Stand on Exercise and Fluid Replacement; product labels (2026). Sodium needs vary 300–1,000 mg/h per ACSM depending on intensity, heat, and individual sweat rate.
How it works
When Electrolyte Replacement Becomes Critical
For exercise under 60 minutes at moderate intensity, most healthy adults can train on water and replenish electrolytes at the next meal. The problem emerges in long sessions, heat, or heavy sweating: that's when real-time replacement is necessary. Sweat sodium concentration varies between 200 and 2,000 mg/L between individuals — "salty sweaters" (those who leave white residue on clothing) lose far more than average.
Electrolyte Replacement Reference Table
| Scenario | Fluid/hour | Sodium/hour | Potassium/hour |
|---|---|---|---|
| < 60 min, low intensity | 400–500 mL water | Not required | Not required |
| 60–120 min, 20–25 °C, moderate | 500–700 mL | 300–600 mg | 150–200 mg |
| 60–120 min, 20–25 °C, high | 600–800 mL | 500–800 mg | 200–300 mg |
| > 120 min, 25–30 °C | 650–850 mL | 600–900 mg | 200–350 mg |
| Ultra / extreme heat (> 30 °C) | 700–1,000 mL | 800–1,200 mg | 250–400 mg |
Sodium Content of Common Sports Drinks
| Product | Sodium (mg/L) | Adequate for long events? |
|---|---|---|
| Plain water | 0 | No (hyponatremia risk) |
| Gatorade / Powerade | ~450 mg | Only for < 90 min |
| LMNT (one packet) | ~1,000 mg / 500 mL | Yes |
| Precision Hydration PH 1000 | ~1,000 mg/L | Yes |
| DIY (1 L water + 1 tsp salt) | ~2,300 mg | Yes, adjust to taste |
How the Calculation Works
The estimate is based on reference rates from the American College of Sports Medicine (ACSM) Position Stand on Fluid Replacement, adjusted by your inputs:
Editorial Note
This calculator is informational. Values are based on population-level reference data. For specific medical conditions (hypertension, kidney disease, diuretic use), consult a physician before changing your hydration strategy.
Worked Example: 70 kg athlete, 2 hours at 25 °C, moderate intensity
Moderate intensity → base sodium: 500 mg/h
Temperature 25 °C (no extreme heat adjustment)
Total sodium: 500 mg/h × 2 h = 1,000 mg
Potassium: 500 × 0.4 × 2 h = 400 mg
Fluid: 750 mL/h × 2 h = 1,500 mL
1,000 mg sodium + 400 mg potassium + 1.5 L fluid
Disclaimer: Los resultados son orientativos y no reemplazan la consulta médica profesional. Antes de tomar decisiones con impacto, consultá con un médico, nutricionista o profesional de la salud matriculado.
Frequently asked questions
How much sodium do I need per hour of exercise?
The ACSM recommends replacing 300–1,000 mg of sodium per hour during prolonged exercise. In average conditions (moderate intensity, 20–25 °C), the typical range is 400–600 mg/h. In extreme heat (> 30 °C) or high intensity, sodium needs can rise to 800–1,200 mg/h. 'Salty sweaters' — athletes who leave white residue on their clothing — may need even more and should consider individual sweat testing.
Why isn't plain water enough during a marathon or long race?
Drinking large amounts of plain water during prolonged exercise dilutes blood sodium, causing exercise-associated hyponatremia (EAH). Symptoms range from nausea and swelling to seizures and fatal brain edema. The 2015 EAH Consensus Conference documented deaths in previously healthy athletes who drank only water. Co-ingesting sodium with fluid maintains plasma osmolality and prevents this emergency. The bottom line: in any event over 90 minutes, electrolytes are not optional.
How do I know if I'm a salty sweater who needs extra sodium?
The simplest indicator: do you see white residue on your forehead or clothing after training? If yes, you're losing more sodium than average — possibly 1,000–2,000 mg/L of sweat versus 500–800 mg/L typical. The most accurate field method: weigh yourself (naked) before and after a 1-hour effort without drinking anything. Each kilogram lost equals roughly 1 liter of sweat. Divide your estimated sodium loss by that volume to get your approximate sweat sodium concentration.
Are sports drinks like Gatorade or Powerade enough?
For exercise under 90 minutes, generally yes: Gatorade and Powerade provide ~450 mg of sodium per liter, sufficient for shorter sessions. For long events (> 2 hours), extreme heat, or ultra-endurance racing, standard sports drinks fall short. You need more concentrated products (LMNT, Precision Hydration) or a DIY drink: 1 L water + 1 tsp salt + 30 g sugar + lemon juice provides ~2,300 mg sodium at a fraction of the cost.
When do muscle cramps signal an electrolyte deficit?
Electrolyte-related cramps typically appear 60–90 minutes into sustained effort, especially in heat. They're more common in athletes who drink lots of plain water without salts, or those with high sweat rates. The telltale sign: cramps that don't improve with stretching but do improve quickly after taking salt or electrolytes. Potassium also contributes — its deficit causes post-effort fatigue and cramping, remedied by eating a banana or drinking orange juice after training.
What is hyponatremia and what are the warning signs?
Hyponatremia is blood sodium below 135 mmol/L, caused during exercise mainly by drinking excessive plain water. Symptoms progress: first nausea, hand swelling, headache; then confusion, disorientation; in severe cases, seizures and coma. The critical difference from dehydration: a dehydrated athlete improves with fluids; a hyponatremic athlete worsens with more plain water. If EAH is suspected, stop fluid intake and seek emergency medical care immediately.
How much potassium do I actually need to replace during exercise?
Sweat contains far less potassium than sodium: typically 4–8 mmol/L potassium vs. 20–80 mmol/L sodium. For events under 4–5 hours, post-exercise dietary potassium (banana, orange juice, potatoes) is sufficient for most athletes. Active supplementation during exercise matters primarily in ultra-endurance events (12+ hours) or athletes with restricted diets. This calculator estimates potassium at ~40% of the recommended sodium value, aligned with ACSM and ISSN references.
Should I use this calculator differently for training versus racing?
Yes. In training, you can tolerate mild fluid and electrolyte deficits as a controlled stress that promotes heat acclimatization. For racing — especially events over 2 hours — arrive well-hydrated and execute a pre-calculated intake plan from the first 30 minutes (don't wait until you feel thirsty or depleted). Use this calculator in training to establish your baseline, validate it with pre/post weight checks, and refine it before relying on the numbers in competition. Race-day adrenaline and faster pacing typically increase sweat rate beyond equivalent training efforts.
Do medications or health conditions change electrolyte replacement needs?
Yes — significantly. Thiazide diuretics (hydrochlorothiazide) and loop diuretics (furosemide) increase baseline urinary sodium and potassium losses. NSAIDs (ibuprofen, naproxen) reduce renal sodium excretion and increase EAH risk — their use during ultra-endurance events is now discouraged by race medical directors. Kidney disease impairs both sodium and potassium handling. Cystic fibrosis dramatically elevates sweat sodium concentration (3–5× average). Any athlete with a chronic condition or taking regular prescription medications should consult a physician or sports dietitian before applying population-level electrolyte targets.
Can I drink too much during exercise, and how would I know?
Yes. Overdrinking during exercise is a leading cause of EAH. The outdated 'drink ahead of thirst' doctrine from the 1990s has been refuted. Current ACSM guidance recommends drinking to thirst as the primary guide, with pre-calculated targets as a secondary check. Warning signs of overdrinking: weight gain during a race, bloating, nausea without other cause, puffiness in hands or face, very pale urine. Urine should be light lemonade yellow — very pale clear suggests over-hydration; dark amber indicates underhydration.
Sources & references
Methodology & trust
Editorial
Calculadora de salud revisada por el equipo editorial de Hacé Cuentas, contrastada con American College of Sports Medicine — Position Stand on Exercise and Fluid Replacement, según nuestra política editorial y metodología.
Updates
Última revisión: June 20, 2026. Los parámetros se verifican periódicamente con las fuentes citadas.
Privacy
Calculations run 100% in your browser. We do not store or transmit your data.
Limitations
Indicative results. For critical decisions, consult a professional.
📌 How to cite this calculator
Rodríguez, M. (2026). Electrolyte Replacement Calculator for Athletes. Hacé Cuentas. https://hacecuentas.com/electrolyte-replacement-exercise
Contenido bajo licencia CC-BY 4.0 — reutilizable citando la fuente con enlace a Hacé Cuentas.