Health
Daily water intake calculator
Estimate how much water to drink per day based on body weight and exercise level. Output in liters, milliliters, US cups, and US fluid ounces — pick whichever your bottle is marked in.
Formula
Adults need roughly 30–40 ml of water per kg of body weight per day, with the high end if you exercise, live somewhere hot, or eat a low-water-content diet. This calculator uses 35 ml/kg as a midpoint baseline and adds an activity bonus from the American College of Sports Medicine (300–750 ml depending on duration).
The number includes water from all sources — coffee, tea, juice, and water-rich foods (cucumber, watermelon, soup) all count. The old '8 glasses a day' rule is a rough approximation that happens to match this formula for a ~65 kg person. Pregnancy adds ~300 ml/day; lactation adds ~700 ml/day. Hot climate or fever can double the requirement.
Thirst is a slightly delayed signal but a good one — drink when thirsty, drink before exercise, and watch your urine: pale yellow = hydrated, dark yellow = drink more.
Examples
- 0170 kg, moderate activity→ 70 × 35 + 500 = 2950 ml ≈ 2.95 L
- 0260 kg, sedentary→ 60 × 35 = 2100 ml = 2.1 L
- 0385 kg, heavy activity→ 85 × 35 + 750 = 3725 ml ≈ 3.73 L
FAQ
- Yes — hyponatremia (dangerously low sodium) is possible if you drink large amounts very quickly without electrolytes, usually during endurance events. For normal day-to-day drinking, the kidneys can handle 5–10 L/day without issue.