Water Intake Calculator: How Much Should You Drink?

Fluid needs grow with body size, exercise and heat. Enter your weight, how long you exercise and your climate to get a daily fluid target in litres and in glasses.

FreeNo sign-upRuns in your browserUpdated 2 Nov 2026
kg
min
Total minutes of exercise or physical work.
Your resultLive

Educational estimate only. It is not medical advice or a diagnosis. Talk to a doctor or registered dietitian before changing your diet or exercise.

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How to use this calculator

  1. Enter your body weight.
  2. Enter the minutes you exercise or work physically in a day.
  3. Choose your climate.
  4. Read the daily target and spread it across the day.

The formula

Base need = 33 ml × body weight in kg. Exercise adds 350 ml for every 30 minutes. Hot or humid weather adds 500 ml. Total = base + exercise + climate. A glass is taken as 250 ml.

Worked example

A 70 kg person who exercises 30 minutes a day in hot weather: base = 70 × 33 = 2,310 ml, exercise adds 350 ml and the climate adds 500 ml. The total is 3,160 ml, about 3.2 litres or 13 glasses. Without extras the usual range is 2.1 to 2.5 litres.

Understanding your result

This is total fluid, and tea, milk, buttermilk and the water in food all count. Pale yellow urine is a simple sign you are well hydrated. Thirst, heat, illness and pregnancy change needs, so use the figure as a guide and not a strict target.

When to use it

  • Set a daily hydration target.
  • Adjust for summer or heavy exercise.
  • Build a habit with a number of glasses.

Assumptions and limits

Educational estimate, not medical advice. A doctor or registered dietitian can give guidance that fits your health. People with heart, kidney or liver conditions, or on fluid limits, should follow their doctor's advice. Drinking very large amounts quickly can be harmful.

Frequently asked questions

Do I need to drink 8 glasses?

That is a handy rule, but your own number depends on size, activity and climate.

Does tea or coffee count?

Yes, they contribute to your fluid, though plain water is a good base.

How do I know I am drinking enough?

Pale yellow urine and no strong thirst are good signs.

Do I need more when I exercise?

Yes. The calculator adds 350 ml for every 30 minutes.

Can I drink too much water?

Yes, in extreme amounts. Sip steadily through the day.