Water Intake Calculator
Estimate your daily water needs based on body weight and exercise time.
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2,670 ml
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Formula
Examples
| Input | Result |
|---|---|
| Weight 70 kg, little exercise (baseline 35 ml/kg) | About 2450 ml — roughly 2.5 litres per day |
| Weight 70 kg plus 30 minutes of exercise (+500 ml) | About 2950 ml — roughly 3.0 litres per day |
| Weight 90 kg, little exercise (35 ml/kg) | About 3150 ml — roughly 3.2 litres per day |
About this calculator
A water intake calculator estimates how much fluid you should drink each day to stay properly hydrated, based mainly on your body weight and how much you exercise. Adequate hydration supports nearly every body function, from regulating temperature and lubricating joints to transporting nutrients and keeping your energy and concentration steady.
The most common approach bases your baseline on body weight, using roughly 30 to 35 millilitres of water per kilogram (about half an ounce per pound). On top of that baseline, the calculator adds extra fluid for physical activity, since you lose water through sweat — a common rule is an additional 350 to 700 ml for every 30 to 60 minutes of exercise. Hot or humid weather, high altitude, illness with fever, and pregnancy or breastfeeding all push the requirement higher still.
To use the tool, enter your weight and choose your unit system, then indicate your daily exercise duration or activity level. The calculator returns a recommended daily target, usually in litres and the equivalent number of glasses, so it is easy to translate into a habit.
Interpret the figure as a total fluid goal rather than a strict quota of plain water. Around 20 percent of your intake typically comes from food, especially fruits and vegetables, and other drinks count too. A practical way to check hydration is urine colour: pale straw means you are on track, while dark yellow signals you should drink more.
Use common sense around the number. The old "eight glasses a day" rule is just a rough average, and individual needs vary widely. Spread intake across the day instead of gulping large amounts at once, drink more before and during exercise and heat, and avoid forcing far beyond thirst, since drinking extreme volumes very quickly can dangerously dilute blood sodium.
Frequently asked questions
A common baseline is about 30 to 35 ml of fluid per kilogram of body weight, so a 70 kg adult needs roughly 2.4 to 2.5 litres a day before exercise. Add more for workouts, hot weather, illness or pregnancy, and remember food and other drinks contribute too.
Yes. Most beverages, including coffee and tea, hydrate you despite mild diuretic effects, and water-rich foods like fruit, vegetables and soups can supply around 20 percent of your daily fluid. The calculator targets total fluid, not just plain water from a glass.
Roughly 350 to 700 ml of extra fluid for every 30 to 60 minutes of exercise is a good guide, more in heat or for heavy sweaters. Drink some before, sip during long sessions, and rehydrate afterwards; weighing yourself before and after shows how much you lost.
Yes, though it is uncommon. Drinking very large volumes in a short time can dilute blood sodium and cause hyponatremia, which is dangerous. Spread your intake through the day, generally drink to thirst plus your activity needs, and avoid forcing litres at once.
Urine colour is the simplest gauge: pale, straw-coloured urine usually means good hydration, while dark yellow suggests you need more fluid. Persistent thirst, headaches, dry lips and fatigue are other signs you may be running low.
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