Water Intake Calculator

Estimate how much water you should drink each day based on your body weight and activity.

kilograms

minutes per day

Please enter a valid weight.

Daily Water Intake
—L
— ml · about — cups
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How much water do you really need?

Water is essential for nearly every function in your body — regulating temperature, transporting nutrients, cushioning joints, and removing waste. But the famous "eight glasses a day" rule is a one-size-fits-all guideline that ignores your body size and lifestyle. A more personalised estimate scales with your weight and how much you sweat, which is exactly what this calculator does.

How it's calculated

This tool uses a widely cited estimate of roughly 33 ml of water per kilogram of body weight, then adds about 350 ml for every 30 minutes of exercise to replace fluid lost through sweat:

  • Baseline = weight (kg) × 33 ml
  • Exercise add-on = (minutes ÷ 30) × 350 ml

For example, a 70 kg person who exercises 30 minutes a day needs about 2.31 L baseline + 0.35 L = roughly 2.66 litres per day.

Factors that increase your needs

  • Hot or humid weather — more sweating means more replacement
  • High altitude — increases fluid loss
  • Illness — fever, vomiting, or diarrhoea raise needs
  • Pregnancy and breastfeeding — require additional fluid
  • High-protein or high-fibre diets — need more water to process

Tips to stay hydrated

You don't have to drink it all as plain water — tea, milk, and water-rich foods like fruit and vegetables all count toward your total. Spread intake throughout the day rather than gulping large amounts at once, keep a bottle visible as a reminder, and use urine colour as a simple gauge: pale straw-yellow means you're well hydrated.

Frequently asked questions

How much water should I drink a day?

A common evidence-based estimate is about 33 ml of water per kilogram of body weight per day, plus roughly 350 ml for every 30 minutes of exercise. For a 70 kg person that's around 2.3 litres baseline. Needs rise with heat, altitude, illness, and pregnancy.

Is the 8 glasses a day rule true?

The 8×8 rule (eight 8-ounce glasses, about 2 litres) is a rough guideline, not a scientific requirement. Actual needs depend on body size, activity, climate, and diet. Calculating based on body weight, as this tool does, gives a more personalised estimate.

Does food and other drinks count toward hydration?

Yes. Roughly 20% of daily fluid typically comes from food, especially fruits and vegetables, and drinks like tea, milk, and juice also count. This calculator estimates total water intake; you don't need to drink all of it as plain water.

Can I drink too much water?

Yes, though it's rare. Drinking extreme amounts in a short time can dilute blood sodium (hyponatremia), which is dangerous. Spread your intake through the day and let thirst and urine colour (pale yellow is ideal) guide you.

How do I know if I'm hydrated?

The simplest check is urine colour: pale straw-yellow usually means well hydrated, while dark yellow suggests you need more fluid. Thirst, dry mouth, headache, and fatigue can also be signs of dehydration.

Disclaimer: This calculator provides a general estimate and is not medical advice. Individual hydration needs vary. People with kidney, heart, or other medical conditions should follow their doctor's fluid guidance.

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