Water Intake Calculator

How It Works

The general guideline of "8 glasses a day" is a starting point, but your actual water needs depend on your body weight, activity level, climate, and diet. A common evidence-based approach is 33 ml per kg of body weight as a baseline, then adjusting upward for exercise, hot weather, and caffeine intake (which has a mild diuretic effect). You lose water through breathing, sweating, and digestion. During exercise, you can lose 0.5 to 2 liters per hour through sweat. Signs of dehydration include dark yellow urine, thirst, headaches, and fatigue. On the other hand, overhydration (hyponatremia) is rare but serious — do not force excessive water intake beyond thirst. Food provides about 20% of daily water intake, especially fruits and vegetables.