Water Intake Calculator – Daily Water Needs
Calculate your optimal daily water intake based on your body weight and activity level. Get personalized hydration recommendations in liters or cups.
💡 Drinking water recommendation: 30-33 mL per kg of body weight. This excludes water from food sources. Adjust based on activity level, climate, and individual needs.
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How Much Water Do You Actually Need?
The commonly cited "8 glasses a day" rule lacks scientific basis. The US National Academies recommend about 3.7 liters/day for men and 2.7 liters/day for women total water intake — including water from food (about 20% of intake). Actual needs vary with body size, activity, climate, and health status.
Signs of Dehydration
Mild dehydration (1–2% body weight loss in water) causes fatigue, reduced concentration, and headaches. Urine color is the simplest indicator: pale yellow is well-hydrated, dark yellow or amber means drink more. Thirst is a late-stage signal — don't wait until you feel thirsty.
Exercise and Heat Increase Needs
Vigorous exercise increases water needs by 0.5–1 liter per hour. Hot, humid climates increase needs further. Endurance athletes may need electrolyte replacement (sodium, potassium) alongside water to prevent hyponatremia — dangerously low sodium from drinking too much plain water.