How is the target estimated?

The tool multiplies your weight by 35 ml per kilogram, then adds 350 ml for every 30 minutes of daily exercise. The 30–35 ml/kg range is a common rule of thumb in nutrition practice; this calculator uses the upper end. Needs still vary with climate, diet, and health.

Is the “8 glasses a day” rule accurate?

It’s a rough shorthand — 8 glasses of 250 ml is about 2 liters, which suits some people and not others. A weight-based estimate is more personal: a 50 kg and a 100 kg person clearly don’t need the same amount. Thirst and pale-straw urine remain the best day-to-day checks.

Do coffee, tea, and other drinks count?

Yes. Despite caffeine’s mild diuretic effect, caffeinated drinks still add more fluid than they cost, and milk, juices, and soups count too. Plain water is simply the cheapest, calorie-free way to hit the target.

Can I drink too much water?

Yes. Drinking large volumes faster than the kidneys can excrete can dilute blood sodium (hyponatremia), which is dangerous. Spread intake across the day and don’t force liters down in one sitting — more is not automatically better.

Should I drink more when exercising or in the heat?

Yes. The calculator already adds 350 ml per 30 minutes of exercise, but heavy sweating in hot or humid weather raises needs beyond that. For long, intense sessions, fluids with electrolytes make sense; for everyday workouts, water is enough.

When should I ask a doctor instead of using a calculator?

If you have kidney, heart, or liver disease, take diuretics, are pregnant or breastfeeding, or have been told to restrict fluids. In those cases your care team’s target overrides any rule of thumb — including this one.

No — the estimate is calculated entirely in your browser. Your weight and exercise minutes are never sent to a server.

Water Intake Calculator

Estimate how much water to drink daily based on your weight and exercise.

Runs in your browser — files never leave your device

WeightkgExercisemin/day

Daily water

2.8 L

Glasses (250 ml)

How it works

This tool estimates how much fluid to aim for in a day, based on the two factors that matter most for most healthy adults: body weight and exercise. Bigger bodies turn over more water, and sweat during activity has to be replaced — so a personal target beats a one-size-fits-all number.

The formula: 35 ml of water per kilogram of body weight, plus 350 ml for every 30 minutes of daily exercise. The result is shown in liters (rounded to one decimal place) and as 250 ml glasses (rounded to the nearest glass). The 30–35 ml/kg range is a widely used rule of thumb among nutrition professionals; this calculator uses the upper end.

Worked example: a 70 kg person who exercises 30 minutes a day. 70 × 35 ml = 2450 ml, plus 350 ml for the exercise, makes 2800 ml — the tool shows 2.8 L, or 11 glasses (2.8 ÷ 0.25 = 11.2, rounded to 11).

Treat the number as a whole-day fluid budget rather than a strict count of plain water. Tea, coffee, milk, and soups all contribute, and food — especially fruit and vegetables — typically covers a meaningful share of daily fluid on its own. Practical checks that you’re on track: you rarely feel thirsty, and your urine stays a pale straw color.

Limitations: needs rise with heat, humidity, altitude, fever, vomiting or diarrhea, and during pregnancy or breastfeeding — and some medical conditions (kidney, heart, or liver disease) require deliberately limiting fluids. If your doctor has given you a fluid target, follow it, not a formula. This estimate is general guidance only — not medical advice.

Frequently asked questions

How is the target estimated?: The tool multiplies your weight by 35 ml per kilogram, then adds 350 ml for every 30 minutes of daily exercise. The 30–35 ml/kg range is a common rule of thumb in nutrition practice; this calculator uses the upper end. Needs still vary with climate, diet, and health.
Is the “8 glasses a day” rule accurate?: It’s a rough shorthand — 8 glasses of 250 ml is about 2 liters, which suits some people and not others. A weight-based estimate is more personal: a 50 kg and a 100 kg person clearly don’t need the same amount. Thirst and pale-straw urine remain the best day-to-day checks.
Do coffee, tea, and other drinks count?: Yes. Despite caffeine’s mild diuretic effect, caffeinated drinks still add more fluid than they cost, and milk, juices, and soups count too. Plain water is simply the cheapest, calorie-free way to hit the target.
Can I drink too much water?: Yes. Drinking large volumes faster than the kidneys can excrete can dilute blood sodium (hyponatremia), which is dangerous. Spread intake across the day and don’t force liters down in one sitting — more is not automatically better.
Should I drink more when exercising or in the heat?: Yes. The calculator already adds 350 ml per 30 minutes of exercise, but heavy sweating in hot or humid weather raises needs beyond that. For long, intense sessions, fluids with electrolytes make sense; for everyday workouts, water is enough.
When should I ask a doctor instead of using a calculator?: If you have kidney, heart, or liver disease, take diuretics, are pregnant or breastfeeding, or have been told to restrict fluids. In those cases your care team’s target overrides any rule of thumb — including this one.
Is my data uploaded?: No — the estimate is calculated entirely in your browser. Your weight and exercise minutes are never sent to a server.

Water Intake Calculator

How it works

Frequently asked questions

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