Water Intake Calculator

There is no single amount of water that suits everyone. Bigger bodies, exercise, hot weather, pregnancy and breastfeeding all raise your needs. This calculator gives a personal daily estimate in litres, cups and ounces.

How to use the water calculator

1. Enter your body weight.
2. Add how many minutes you exercise on a typical day.
3. Choose your weather and whether you are pregnant or breastfeeding.

How it works

• Baseline: about 33 ml of fluid per kg of body weight (a common rule of thumb of 30–35 ml/kg).
• Exercise: about 350 ml extra for every 30 minutes.
• Hot or humid weather: about 500 ml extra.
• Pregnancy: about 300 ml extra. Breastfeeding: about 700 ml extra.

For comparison, the U.S. National Academies suggest a total water intake (from drinks and food) of about 3.7 litres a day for men and 2.7 litres for women. Around 20% of that usually comes from food.

Example

A 70 kg person who exercises for 30 minutes a day in mild weather needs about 2.3 litres of baseline fluid plus 0.35 litres for exercise: roughly 2.7 litres, or about 11 cups.

Frequently asked questions

Do tea and coffee count?

Yes. Although caffeine has a mild effect on urine, tea and coffee still add to your daily fluid. Water, milk and soups count too.

How can I tell if I am drinking enough?

Pale yellow urine and rarely feeling thirsty are good signs. Dark urine, headaches and tiredness can mean you need more.

Can you drink too much water?

Yes, though it is rare. Drinking very large amounts quickly, especially during long endurance events, can lower blood sodium. Drink to thirst and don’t force large volumes.

Sources

• National Academies of Sciences – Dietary Reference Intakes for water
• European Food Safety Authority (EFSA) – water intake for pregnancy and breastfeeding
• American College of Sports Medicine – fluid replacement during exercise

People with heart failure or kidney disease may need to limit fluids. Follow your doctor’s advice.