Is 8 glasses a day accurate?
It's a rough guide. Individual needs vary by size, activity, and climate—use body weight formula.
Health Fitness
Hydration Calculator
Estimate hydration with quick inputs.
Fast, practical estimates
Adjust inputs for the most useful result.
What this calculator does
A hydration calculator determines daily water intake needs based on body weight, activity level, and climate. Base recommendation is 30-35 ml per kg body weight, with adjustments for exercise, heat, and altitude.
How it works
Calculate baseline from body weight, then add for activity (400-800 ml/hour exercise) and environment (+10-25% for heat/altitude).
Formula
Base: 30-35 ml × Weight (kg). Exercise: +400-800 ml/hour. Hot climate: +10-15%. Altitude: +20-30%.
Tips for using this calculator
- Drink before you feel thirsty
- Urine color indicates hydration (pale yellow = good)
- Coffee and tea count toward intake
- Electrolytes needed for exercise >1 hour
- Overhydration (hyponatremia) is possible—don't overdo it
Frequently asked questions
Do coffee and tea count?
Yes, caffeinated beverages still hydrate despite mild diuretic effect.
Can I drink too much water?
Yes, hyponatremia (low sodium) can occur. Spread intake throughout day; don't chug large amounts.