Hydration Calculator
How much water do you actually need?
The '8 glasses a day' rule is a rough average, not a medical standard. Individual needs vary with body size, activity level, climate, and diet (food contributes ~20% of water intake). The best daily indicator isn't volume drunk — it's urine color. Pale yellow means hydrated; dark yellow means drink more.
Hydration matters most during exercise and heat. Endurance athletes can lose 1–2 liters per hour in hot conditions; beyond ~90 minutes of sweating, add electrolytes to prevent hyponatremia. Alcohol and caffeine are mild diuretics — not dehydrating in typical doses, but worth noting on heavy days.
Frequently asked questions
Do I really need 8 glasses a day?
The '8×8' rule is a rough average, not a medical mandate. Individual needs vary with body size, activity, climate, and diet (food contributes ~20% of water). A better indicator is urine color: pale straw yellow = adequate; dark yellow = drink more; clear and constant = probably over-drinking.
When does hydration matter most?
Heat, exercise, and altitude. Endurance athletes can lose 1–2 L/hour of sweat in hot conditions. Airplanes are humidity-negative environments. Alcohol is a diuretic. On hot-exercise or alcohol-heavy days, intentionally bump intake 1–2 liters.
What are electrolytes and when do I need them?
Sodium, potassium, magnesium, calcium — minerals that maintain nerve and muscle function. Lost in sweat. For exercise under 90 minutes in mild weather, water alone is fine. Beyond that, or in heat, add sports drink, electrolyte tablets, or salty snacks to prevent hyponatremia (low blood sodium).
Can I over-drink?
Yes — water intoxication (hyponatremia) is possible and dangerous. Kidneys process about 0.8–1.0 L/hour max. Marathon runners occasionally hospitalize themselves by drinking too much plain water during races. If you're drinking enough to pee clear every hour, you may be overdoing it.
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