Calculator Nutrition
Water intake calculator
The "eight glasses a day" rule is a myth — real needs scale with your body weight, how much you sweat, and the heat around you. Enter a few details for a sensible daily target.
Your daily water target
0liters/day
By the numbers Context
How much water you really need
Hydration advice is full of round numbers that were never based on much. The famous “eight glasses a day” has no strong scientific backing, and it ignores the two things that actually move your needs: how much you sweat and how much you weigh. This calculator scales a baseline by your body weight, then adds for exercise and climate.
It also helps to know that all fluids count toward hydration — tea, coffee, and the water in food, which supplies roughly a fifth of your intake. The U.S. National Academies of Sciences put adequate total water at about 2.7 litres a day for women and 3.7 for men, from all sources combined. Rather than chase an exact figure, most people can trust thirst and aim for pale-yellow urine, drinking extra around workouts and heat.
2.7 / 3.7 L
suggested total daily water for women / men, from all sources
U.S. National Academies
~20%
of your daily water that comes from food
Research
Myth
the "8 glasses a day" rule — no strong evidence behind it
Research
Sources: U.S. National Academies of Sciences, Engineering, and Medicine (dietary reference intakes for water).
Frequently asked questions
How much water should I drink a day?
It depends on your weight, activity, and climate. As a general anchor, the U.S. National Academies suggest about 2.7 litres for women and 3.7 for men in total each day — but that includes water from food and all drinks, not just plain water.
Is 64 oz of water a day enough?
For a smaller, less active person in a mild climate, 64 oz (about 1.9 litres) of drinking water may be plenty, especially with water from food on top. For larger or very active people, or in the heat, it is likely on the low side.
Is 2 litres of water a day enough?
For many people, 2 litres of drinking water plus the water in food is adequate. Needs rise with body size, exercise, and heat, so use thirst and urine colour as a check.
Does the "8 glasses a day" rule apply to everyone?
No. It is a memorable rule of thumb, not a scientific requirement. Actual needs vary widely with body size and activity, and food and other drinks count toward the total.
How can I tell if I am drinking enough?
Pale-yellow urine and rarely feeling thirsty are good signs you are well hydrated. Dark urine, headaches, or persistent thirst suggest you need more.