Water Intake Calculator

The calculator multiplies your weight by 35 mL per kg as a baseline, then adds 500 mL for each hour of exercise and another 500 mL for a hot-climate selection. It also treats a cup as 240 mL. These are fixed planning heuristics, not medical prescriptions. Pregnancy, kidney or heart disease, medications, diet, humidity, illness, and exercise conditions can require a different intake.

The "8 x 8" rule is not a National Academies requirement. Adequate Intake values refer to total water from beverages and food and are population references rather than exact personal targets. This calculator's weight-based formula is also an estimate and is not necessarily more accurate for an individual with unusual health, climate, or activity needs.

Coffee and tea generally contribute fluid despite caffeine's mild diuretic effect at typical doses. Alcohol can increase urine output, but whether a drink creates a net fluid loss depends on dose, concentration, food, and the person's condition. Do not use alcoholic drinks as a hydration strategy, and do not subtract a fixed volume from this calculator.

Thirst, reduced urine output, dry mouth, dizziness, and darker urine can occur with dehydration, but none is diagnostic by itself. Urine color also changes with food, supplements, medications, and illness. Seek medical advice for persistent symptoms, confusion, fainting, inability to keep fluids down, or signs of severe dehydration rather than relying on the calculator.

Yes. Drinking very large amounts in a short window can dilute blood sodium to dangerous levels, a condition called hyponatremia. It can affect endurance athletes and hikers who overdrink, and sports drinks do not reliably prevent it. Do not force fluids. During prolonged exercise or heat, drink to thirst and seek urgent care for confusion, seizures, or loss of consciousness.