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General guidelines suggest 2.0–3.7 liters (8–16 cups) per day for adults, but your ideal intake depends on body weight, activity level, climate, and diet. A common formula is 0.033 liters per kilogram of body weight as a baseline, then adjusting upward for exercise, heat, and other factors. This calculator personalizes your target based on your specific inputs.
Caffeinated beverages like coffee and tea do contribute to hydration, but caffeine has a mild diuretic effect. For every caffeinated drink you consume, adding about 150ml (half a cup) of extra water compensates for this effect. Our calculator automatically adjusts your target based on your reported caffeinated drinks.
Exercise significantly increases water needs. Light activity adds roughly 350ml daily. Moderate exercise (30–60 min/day) adds 500–700ml. Intense training can require an additional 1–1.5 liters or more. Drink before, during, and after exercise for best results.
Early signs include dark urine (pale yellow is ideal), thirst, dry mouth, fatigue, and difficulty concentrating. Even mild dehydration of 1–2% of body weight can impair cognitive performance and endurance. The simplest check: pale yellow urine means you're well hydrated.