Sports Hydration Calculator
Calculate fluid and electrolyte needs from exercise duration, intensity, and temperature.
Returns hourly water, sodium, and carb targets for endurance events.
Sports drink electrolyte and carbohydrate calculation determines the optimal concentration and volume of fluids to maintain performance during exercise. The goal is to replace sweat losses, maintain blood glucose, and preserve electrolyte balance — without overhydrating.
Carbohydrate concentration formula: Carb Concentration (%) = (Carbs in grams ÷ Volume in mL) × 100
Optimal range: 6–8% carbohydrate concentration for gastric emptying and fuel delivery.
- Below 6%: inadequate fueling for endurance exercise beyond 90 minutes
- Above 8–10%: slows gastric emptying; causes GI distress
Electrolyte replacement rates (per hour of exercise):
- Sodium: 500–1,000 mg/hour (sweat concentration: 20–80 mmol/L)
- Potassium: 100–200 mg/hour
- Magnesium: 30–50 mg/hour
- Chloride: replaced proportionally with sodium
Fluid intake formula: Hourly Intake Target = Sweat Rate (mL/hour) × 75–80%
Full replacement is not recommended — slight fluid deficit is normal and safe during exercise.
Sweat rate estimation: Weigh before and after a 1-hour training session (without drinking). Each 1 kg (2.2 lbs) of weight lost ≈ 1 liter of sweat.
DIY sports drink formula (per 500 mL water):
- Carbohydrate: 30–40 g (table sugar, maltodextrin, or honey)
- Sodium: 250–400 mg (0.5–0.8 g table salt = 0.65 g salt)
- Potassium: 50–100 mg (a small pinch of NoSalt/KCl)
- Optional: lemon juice for flavor and palatability
What each variable means:
- Isotonic solution — same concentration as blood (~280–300 mOsm/kg); absorbed quickly; ideal for during exercise
- Hypertonic — higher concentration than blood (>8% carbs); absorbed more slowly; used for recovery fueling after exercise
- Hypotonic — lower concentration than blood; absorbed fastest; good for rapid hydration but minimal fueling
Worked example: Cyclist, 2-hour ride at moderate intensity. Estimated sweat rate: 1.2 L/hour.
Total fluid target = 2 hours × 1.2 L × 0.75 = 1.8 liters (900 mL per hour) Carbs needed (at 7%): 900 mL × 0.07 = 63 g carbs/hour → 126 g total Sodium: 700 mg/hour × 2 = 1,400 mg total sodium (about 3.5 g table salt equivalent)
DIY mix for 1.8 liters: 126 g sugar + 3.5 g salt + water to 1,800 mL. Cost: ~$0.25 vs $4–$6 for commercial sports drinks.