Water Intake Calculator

Daily water requirements depend on body size, climate, activity, and diet. A practical baseline uses body weight: base intake (liters) = weight (kg) × 0.033. This gives roughly 33 ml per kg — close to the often-cited 30–35 ml/kg range used in sports nutrition. Activity level then adjusts the base: sedentary × 1.0, light activity × 1.1, moderate × 1.2, active × 1.3, very active × 1.4.

For a 70 kg person with moderate activity: base = 70 × 0.033 = 2.31 liters. Apply the moderate multiplier: 2.31 × 1.2 ≈ 2.77 liters, typically presented as roughly 2.5–2.8 L/day. In cups (240 ml each), that is about 10–12 cups. The "8 glasses a day" rule (≈ 1.9 L) is a rough minimum for smaller sedentary adults but falls short for larger or active individuals.

Water needs rise in hot weather, at altitude, during illness with fever, and in pregnancy or breastfeeding. Roughly 20% of daily fluid often comes from food — fruits, vegetables, soups, and yogurt all contribute. Caffeinated drinks provide net hydration despite mild diuretic effects at normal consumption levels. Thirst is a reliable short-term signal, but athletes and older adults may benefit from scheduled drinking before thirst kicks in.

Signs of adequate hydration include pale yellow urine (not clear, not dark amber), normal energy levels, and infrequent headaches related to dehydration. Overhydration (hyponatremia) from excessive plain water during endurance events is rare but serious — drink to thirst during most activities and include electrolytes during prolonged heavy sweating.

Enter your weight and typical activity level to get a personalized daily water target in liters, milliliters, and cups. Spread intake across the day, drink extra around workouts, and adjust upward in summer heat or if urine stays consistently dark despite meeting the calculated target.