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How Much Water Should You Drink Per Day?
The National Academies of Sciences recommends about 3.7 liters (125 oz) per day for men and 2.7 liters (91 oz) per day for women from all beverages and food. The "8 glasses a day" rule is a simplified guideline — actual needs vary significantly based on body size, activity, and climate.
The 0.5 oz Per Pound Rule
A widely used baseline: drink 0.5 oz of water per pound of body weight per day. A 150-pound person would need about 75 oz (about 9.4 cups). This calculator uses this formula adjusted for activity, climate, and special conditions.
Signs of Dehydration
- Dark yellow urine (well-hydrated urine is pale yellow)
- Fatigue, headaches, dizziness
- Dry mouth or lips
- Decreased athletic performance
- Poor concentration
Does Coffee Count?
Yes. Despite its mild diuretic effect, research shows caffeinated beverages like coffee and tea contribute to your daily fluid intake. Alcohol, however, is dehydrating and should not count toward your goal.