Sweat Rate Calculator
Calculate your sweat rate during exercise using pre and post-workout weigh-ins. Determine fluid replacement needs to optimize performance and prevent dehydration.
Electrolyte Replacement Calculator
Estimate sodium, potassium, and magnesium losses from sweat during exercise. Get personalized electrolyte replacement recommendations based on your sweat rate.
⚠️ Medical Disclaimer: Electrolyte estimates are approximate. Individual sweat composition varies widely. Consult a sports dietitian for precision. People with hypertension, kidney disease, or heart conditions should follow their doctor's sodium guidance.
L/hr
min
Sodium (Na⁺)
1,080
mg lost
Potassium (K⁺)
432
mg lost
Magnesium (Mg²⁺)
32
mg lost
Total Sweat Volume⧉
1.8 L
1.5 hrs at 1.2 L/hr
Na During Exercise⧉
300–600 mg/hr
Target intake rate
Post-Exercise Na⧉
1,080–1,620 mg
100–150% replacement
Salt Equivalent⧉
0.5 tsp
Table salt for total loss
Electrolyte Food & Drink Sources
| Source | Na (mg) | K (mg) | Mg (mg) |
|---|---|---|---|
| Sports Drink (500 mL) | 230 | 60 | 0 |
| 1/4 tsp Table Salt | 590 | 0 | 0 |
| Banana (1 medium) | 1 | 422 | 32 |
| Coconut Water (240 mL) | 252 | 600 | 60 |
| Salted Pretzels (30g) | 490 | 24 | 7 |
| Pickle Juice (60 mL) | 400 | 12 | 3 |
| Electrolyte Tablet (1) | 300 | 75 | 25 |
| Cheese (1 oz) | 175 | 27 | 8 |
Timing Strategy
| When | Sodium Target | Best Sources |
|---|---|---|
| 2–3h Before | 300–600 mg with 500 mL water | Salty snack + water |
| During (>60 min) | 300–600 mg/hr in fluid | Sports drink, electrolyte tabs, gels |
| Within 2h After | 1,080–1,620 mg total | Recovery meal with salt, soup, salty snacks |
Planning notes, formulas, and examples
About the Electrolyte Replacement Calculator
This calculator estimates sodium, potassium, and magnesium losses during a workout from sweat rate, duration, and sweat sodium category, then turns those losses into a replacement target. It is intended for exercise planning, especially for longer or hotter sessions, not for diagnosing cramps or medical electrolyte problems.
The result is a practical estimate rather than a measured sweat test. It works best when you want a starting point for training or race fueling and know roughly how much you sweat.
When This Page Helps
For shorter sessions, water may be enough; for longer or hotter sessions, sodium loss becomes more relevant. This page gives a practical starting range for replacement instead of assuming one sports-drink recipe fits everyone.
How to Use the Inputs
- Enter your estimated sweat rate (L/hr) from the Sweat Rate Calculator.
- Select your sweat sodium level (low, average, or high/salty sweater).
- Enter the planned or completed exercise duration in minutes.
- Select exercise intensity to factor potassium and magnesium losses.
- View your estimated electrolyte losses and replacement targets.
- Check the food/supplement sources table for practical replacement options.
Formula used
Sodium Loss (mg) = Sweat Rate (L/hr) × Sweat [Na⁺] (mg/L) × Duration (hr)
Potassium Loss (mg) = Sweat Rate × ~200 mg/L × Duration
Magnesium Loss (mg) = Sweat Rate × ~15 mg/L × Duration
Typical Sweat Sodium Concentrations:
• Low: ~300 mg/L
• Average: ~600 mg/L
• High (salty sweater): ~1,100 mg/L
Replacement Window:
• During exercise (>60 min): 300–600 mg Na/hr
• Post-exercise: Replace 100–150% of losses over 4–6 hoursExample Calculation
Result: Na loss: 1,080 mg | K loss: 360 mg | Mg loss: 27 mg
Sweat volume = 1.2 L/hr × 1.5 hrs = 1.8 L total. Sodium = 1.8 × 600 = 1,080 mg. Potassium = 1.8 × 200 = 360 mg. Magnesium = 1.8 × 15 = 27 mg. During the 90-minute session, aim for 450–900 mg sodium intake (300–600 mg/hr). Post-exercise, consume 1,080–1,620 mg sodium through food and fluids.
Tips & Best Practices
- If you see white salt rings on your clothes after exercise, you're likely a salty sweater — select the "High" sodium option.
- For exercise under 60 minutes, water alone is usually sufficient. Electrolyte replacement becomes critical for sessions >60–90 minutes.
- Mix electrolytes into your water rather than taking salt tablets with plain water to improve absorption and reduce GI distress.
- Post-exercise meals naturally contain electrolytes. A meal with 1/4 teaspoon salt has ~600 mg sodium.
- Avoid consuming high-sodium electrolyte products at rest — they're designed for exercise conditions.
- Practice your electrolyte strategy during training, not during races or competitions, to test GI tolerance.
Sodium and Performance
Sodium is the main electrolyte to plan around during prolonged exercise. It helps maintain blood volume, supports fluid absorption in the gut, and contributes to muscle and nerve function. Sodium losses of 3–4 grams during a marathon are common for average sweaters, and salty sweaters can lose substantially more. Inadequate replacement can contribute to progressive performance decline, cramps, and GI distress.
DIY Electrolyte Drinks
A simple homemade electrolyte drink: 500 mL water + 1/4 teaspoon salt (~590 mg Na) + 2 tablespoons honey (30g carbs) + squeeze of lemon. This provides approximately 1,180 mg Na/L, suitable for salty sweaters. For average sweaters, use 1/8 teaspoon salt per 500 mL.
Race Day Strategy
For events lasting 2+ hours, plan electrolyte intake in advance: 300–600 mg sodium per hour, consumed in small frequent doses every 15–20 minutes alongside fluid. Test the strategy during training runs at race intensity. GI tolerance varies significantly between individuals, and race day is not the time to experiment.
Sources & Methodology
Last updated:
Methodology
The calculator multiplies sweat rate by exercise duration and then applies approximate electrolyte concentrations for low, average, or high sodium sweaters. Potassium and magnesium are estimated with conservative exercise-loss assumptions so the output stays useful for planning rather than overstating precision. The result is a replacement guide for training or recovery, not a medical diagnosis of electrolyte status.
Sources
- American College of Sports Medicine position stand. Exercise and fluid replacement (PubMed / Medicine & Science in Sports & Exercise) — Core exercise-hydration guidance and sodium replacement framing.
- Exercise intensity effects on total sweat electrolyte losses and regional vs. whole-body sweat [Na+], [Cl-], and [K+] (PubMed) — Supports the idea that sweat electrolyte losses vary by intensity and measurement method.
- Fluid replacement during exercise (PubMed) — Background on fluid and electrolyte replacement during exercise.
Frequently Asked Questions
Signs include: white residue or stains on dark workout clothes, sweat that stings your eyes or any cuts, a preference for salty foods after exercise, frequent muscle cramps during prolonged activity, and sweat that tastes noticeably salty. You can also get a clinical sweat test for precise sodium concentration measurement.
Absolutely. Post-exercise, whole foods are an excellent electrolyte source. A typical recovery meal with soup, bread with salt, cheese, and a banana can replace most electrolyte losses. However, during exercise, concentrated liquid or tablet sources are more practical since they're easier to consume and absorb.
Standard sports drinks contain about 400–500 mg sodium per liter — adequate for average sweaters but insufficient for salty sweaters during intense exercise. They also provide carbohydrates (6–8%) which help fuel exercise. For heavy sodium losers, consider adding extra sodium to a sports drink or using higher-sodium products.
EAH occurs when blood sodium drops below 135 mmol/L, typically from drinking excessive plain water without adequate sodium during prolonged exercise. Symptoms include nausea, headache, confusion, and in severe cases, seizures and death. It's more common in endurance events lasting >4 hours and in slower participants who have more time to drink.
For most people, a balanced diet provides adequate potassium and magnesium. Sweat losses of these minerals are relatively small compared to sodium. However, prolonged exercise (>2–3 hours) in heat can deplete stores. Including banana, coconut water, or electrolyte products with K and Mg during ultra-endurance events is reasonable.
One quarter teaspoon of table salt (NaCl) contains approximately 590 mg of sodium. A full teaspoon has about 2,360 mg. This is useful for DIY sports drinks: 1/4 teaspoon salt + 2 tablespoons honey in 500 mL water creates an effective electrolyte solution.
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