How much water should you drink per day? Calculate your optimal daily water intake based on your weight and activity.
This is your minimum daily target. Increase during illness, pregnancy, or very hot weather.
The commonly cited "8 glasses a day" rule is a rough guideline, not a precise scientific recommendation. Your actual hydration needs depend on your body weight, activity level, climate, and overall health. This calculator uses a formula based on body weight (roughly 30-35ml per kilogram of body weight) and adjusts for activity level and climate — giving you a more personalized estimate than generic advice.
The baseline calculation multiplies your body weight by approximately 33ml per kilogram. This baseline is then adjusted upward for physical activity (exercise increases fluid loss through sweat) and for hot or humid climates (which increase insensible water loss through skin and breathing).
Water is the ideal source, but other beverages contribute too — herbal tea, milk, and even coffee (despite its mild diuretic effect, the net hydration contribution is still positive). Foods with high water content — watermelon, cucumber, oranges, soup — also contribute meaningfully to your daily total, typically accounting for 20% of total fluid intake for most people.
Pregnant and breastfeeding women need additional fluid (roughly 300ml and 700-1000ml extra per day respectively). People with fever, vomiting, or diarrhea need to replace additional fluid losses. Those at high altitude lose more fluid through increased respiration. If you have kidney disease, heart failure, or are on fluid-restricted medications, follow your doctor's specific guidance rather than general calculators.
Can you drink too much water? Yes — though it's rare. Hyponatremia (dangerously diluted blood sodium) can occur with extremely excessive intake, typically seen in endurance athletes drinking far beyond thirst cues. For most people eating a normal diet, this isn't a practical concern.
Should I drink water even when not thirsty? Thirst is a reasonably reliable signal for most healthy adults, though it can lag behind actual hydration needs during exercise or heat. Spreading intake throughout the day rather than large amounts at once is generally more comfortable and better absorbed.
Does caffeine dehydrate you? The diuretic effect of caffeine is mild and largely offset by the fluid itself in coffee or tea. Moderate caffeine consumption doesn't cause net dehydration in regular consumers.