Find your daily hydration goal based on your body weight, activity level, and climate.
This calculator uses the body-weight method: Water (ml) = Weight (kg) × 35 ml. An 80 kg person needs approximately 2,800 ml (2.8 litres) per day under normal conditions. For imperial: multiply weight in lbs by 0.5 to get ounces, or weight in lbs × 67 ml.
The 35 ml/kg baseline applies to a sedentary adult in a temperate climate. Exercise increases needs significantly: add approximately 500–750 ml for every hour of moderate exercise, more in hot weather or at high altitude. Total water intake includes all beverages — tea, coffee, milk, and juice count — plus water in solid food (typically 20% of total intake). Plain water remains the best source: it has no calories, no caffeine, and is immediately available. Thirst is generally a reliable indicator of hydration in healthy adults, but the elderly often have a blunted thirst response and should monitor intake more deliberately.
A general guideline is 35 ml per kg of body weight per day. A 70 kg person needs roughly 2,450 ml (about 8 cups). Individual needs vary based on climate, activity level, diet, and health status.
Yes. Despite being mild diuretics, coffee and tea still contribute net fluid to your daily intake. Studies show their diuretic effect is minimal at typical consumption levels (1–3 cups/day). Water-rich foods like fruits and vegetables also count.
Exercise significantly increases water loss through sweat — typically 0.5–1 litre per hour of moderate exercise, more in hot or humid conditions. Add at least 500 ml per hour of moderate activity to your baseline daily intake.
Early signs include thirst, dark yellow urine, fatigue, and headache. Moderate dehydration causes dry mouth, dizziness, and reduced concentration. Urine colour is the easiest self-check — pale yellow indicates good hydration; dark yellow or amber signals you need to drink more.