How much water should you drink a day?

There is no single number that suits everyone. A common rule of thumb is around 35 ml of water per kilogram of body weight, adjusted up for exercise and hot weather. For many adults that works out to roughly 2 to 3 litres (8 to 12 cups) a day from all drinks combined. This calculator personalises that estimate using your weight, how much you exercise, and your climate.

How the calculation works

We start with a baseline of about 35 ml per kilogram of body weight, add roughly 350 ml for every 30 minutes of exercise to replace fluid lost through sweat, then apply a small multiplier for warm or hot climates. The result is your suggested total daily fluid intake. Remember that about a fifth of your daily water usually comes from food, especially fruit and vegetables.

Signs you may need more water

Dark yellow urine, headaches, tiredness, and feeling thirsty are common signs of mild dehydration. A simple check is urine colour — pale straw is ideal. You will also need more fluid when you are ill with a fever, pregnant or breastfeeding, or spending time at high altitude.

Frequently asked questions

Do tea and coffee count?

Yes. Despite the myth, moderate tea and coffee contribute to your daily fluid intake. Water and milk are better everyday choices, and sugary drinks are best limited.

Can you drink too much water?

Very rarely, drinking extreme amounts in a short time can dilute blood sodium (hyponatraemia), which is dangerous. For almost everyone, spreading normal amounts through the day is completely safe.

Disclaimer: This calculator provides estimates for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional with concerns about hydration or health.